# DE-AL Republican nominee?

In 2026

Updated: September 16, 2026

Category: Elections

Tags: Primaries, US Elections

HTML: /markets/elections/primaries/de-al-republican-nominee/

## Short Answer

**Key takeaway.** Joseph Arminio is effectively certain to be the Republican nominee for Delaware's At-Large Congressional District in 2026, with the **market** pricing this outcome at **99.0%**.

## Key Claims (September 2026)

**- - Joseph Arminio secured the nomination, according to the Associated Press's September 15 call.** - Despite the call, some official election results remain uncertified, with **0%** reported.
- John J. Whalen III and Earl Cooper were explicitly excluded by the Associated Press's call.

## Market Behavior & Drivers

The Associated Press's call of the September 15 primary for Joseph Arminio drives the 99c **market** price, despite uncertified results.

This market resolved following confirmation of the election result. The contract's price moved to 99% after The Associated Press called the Delaware At-Large district's Republican primary for Joseph Arminio on the evening of September 15, 2026. This event definitively settled the market question.

Before the primary, the market priced Arminio's chances in the low single digits, trading at 3% as late as September 13. No specific news or polling data cited in the provided context accounts for this low probability assessment ahead of his victory over Earl Cooper and John Whalen III. The general election is expected to heavily favor the Democratic incumbent, Sarah McBride, who was unopposed in her primary.

### Who Wins and Why

| Outcome | Market | Model | Why |
| --- | --- | --- | --- |
| Joseph Arminio | 99.0% | 99.6% | Research does not highlight strong supporting evidence. |
| John J. Whalen III | 1.0% | 0.1% | Research does not highlight strong supporting evidence. |
| Earl Cooper | 0.1% | 0.1% | Research does not highlight strong supporting evidence. |

## Model vs Market

| Outcome | Market Probability | Octagon Model Probability |
| --- | --- | --- |
| Joseph Arminio | 99.0% | 99.6% |
| John J. Whalen III | 1.0% | 0.1% |
| Earl Cooper | 0.1% | 0.1% |
| Lee Murphy | 0.1% | 0.1% |
| Donyale Hall | 0.1% | 0.1% |
| Gavin Solomon | 0.1% | 0.1% |

- Expiration: September 15, 2027

## Significant Price Movements

### Outcome: John J. Whalen III

#### 📉 September 16, 2026: 86.0pp drop

Price decreased from 87.0% to 1.0%

**What happened:** The primary driver for an 86.0 percentage point drop in the "DE-AL Republican nominee?" market for John J. Whalen III on September 16, 2026, cannot be identified from the provided web research. While the Delaware primary election was held on September 15, 2026 [[1]](https://www.ballotready.org/elections/delaware-primary-election-e0a7cd55-85f4-4fed-890f-6685435c03f3), the available information confirms Michael Katz won the Republican nomination for the U.S. Senate, not the At-Large House seat John J. Whalen III sought [[2]](https://whyy.org/articles/election-2026-delaware-primary-senate-republican-winner/)[[3]](https://www.washingtonpost.com/elections/results/2026/09/15/delaware-senate-primary-election-2026-live-results-chris-coons-runs-again/)[[4]](https://www.foxnews.com/politics/gop-anesthesiologist-receives-nod-uphill-race-challenge-top-senate-democrat)[[5]](https://www.coasttv.com/news/michael-katz-wins-republican-primary-for-u-s-senate/article_8265a288-c56c-4dbb-8bef-e3066c32d418.html)[[6]](https://www.delawareonline.com/story/news/politics/elections/2026/07/15/whos-running-in-delawares-federal-statehouse-elections-in-2026/90899410007/)[[7]](https://www.amendment.app/elections/2026/DE/house/dc83e5e0-3ba0-4230-81f6-732e857399ef/6d3933e9-a3ed-4e31-a70c-788fa0557ab5). No credible evidence was found for an 86.0pp price drop or any specific event related to John J. Whalen III in the 2026 election cycle [[8]](https://votes.decisiondeskhq.com/races/2026-11-03/delaware-us-senate-general-election/vote-history)[[9]](https://votes.decisiondeskhq.com/races/2026-11-03/delaware-us-senate-general-election/forecast). Therefore, social media was irrelevant, as the purported price movement itself is unsubstantiated by the provided data.

#### 📈 September 11, 2026: 16.0pp spike

Price increased from 55.0% to 71.0%

**What happened:** The provided web research contains no evidence of social media activity, traditional news, or other factors explaining a 16.0 percentage point spike in the prediction market price for "John J. Whalen III" on September 11, 2026 [[10]](https://ballotpedia.org/September_15,_2026,_election_results). While John J. Whalen III was a candidate in the Republican primary for Delaware's at-large U.S. House seat, which took place on September 15, 2026, he ultimately lost to Joseph Arminio [[11]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/)[[12]](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary)[[10]](https://ballotpedia.org/September_15,_2026,_election_results). Therefore, based on the available information, social media activity appears to be irrelevant to the reported price movement [[10]](https://ballotpedia.org/September_15,_2026,_election_results).

### Outcome: Earl Cooper

#### 📉 September 13, 2026: 15.0pp drop

Price decreased from 30.0% to 15.0%

**What happened:** The provided web research does not corroborate a 15.0 percentage point price drop for Earl Cooper in the 'DE-AL Republican nominee?' prediction market on September 13, 2026 [[13]](https://votes.decisiondeskhq.com/elections/2026-09-15/delaware). While the query appears to conflate political candidate Earl Cooper with a social media influencer feud involving Alix Earle and Alex Cooper, this "Earle-Cooper feud" occurred in early 2026 and is unrelated to the political primary in September 2026 [[14]](https://tldrdailynews.com/news/entertainment/entertainment/no-clear-winner-in-earle-cooper-feud-data-shows-dv1cmhh-ux). Consequently, without evidence of the specified market movement, no primary driver can be identified. Social media activity is irrelevant given the lack of corroboration for the described event.

#### 📈 September 12, 2026: 9.0pp spike

Price increased from 23.0% to 32.0%

**What happened:** The provided sources offer no evidence to corroborate a '9.0 percentage point spike' for Earl Cooper in the 'DE-AL Republican nominee?' market on September 12, 2026 [[10]](https://ballotpedia.org/September_15,_2026,_election_results)[[12]](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary). Earl Cooper was a candidate in the Delaware Republican primary for the U.S. House, which took place on September 15, 2026 [[11]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/)[[15]](https://ballotpedia.org/Republican_Party_primaries_in_Delaware,_2026)[[16]](https://ballotpedia.org/United_States_House_election_in_Delaware,_2026_(September_15_Republican_primary)). As the alleged market movement itself is not supported by the available information, it is not possible to identify a primary driver from the given sources.

#### 📉 September 10, 2026: 22.0pp drop

Price decreased from 60.0% to 38.0%

**What happened:** The provided research indicates there is no evidence of a 22.0 percentage point drop for Earl Cooper on September 10, 2026 [[11]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/). Instead, 22% represents Earl Cooper's final share of the vote in the Delaware Republican primary for the U.S. House of Representatives, which took place five days later on September 15, 2026 [[11]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/). Consequently, identifying a primary driver for the stated market movement on September 10 is not possible based on the available information, as the event itself lacks direct evidentiary support as described. Social media activity, traditional news, or market structure factors cannot be attributed as drivers for an unsupported event.

Sources:

1. [Delaware Primary Election - Tuesday, September 15, 2026 | BallotReady](https://www.ballotready.org/elections/delaware-primary-election-e0a7cd55-85f4-4fed-890f-6685435c03f3)
2. [DE election 2026: TK wins GOP Senate primary - WHYY](https://whyy.org/articles/election-2026-delaware-primary-senate-republican-winner/)
3. [Live results: Delaware U.S. Senate primary election 2026](https://www.washingtonpost.com/elections/results/2026/09/15/delaware-senate-primary-election-2026-live-results-chris-coons-runs-again/)
4. [Former Democrat wins GOP US Senate nod in deep-blue Delaware | Fox News](https://www.foxnews.com/politics/gop-anesthesiologist-receives-nod-uphill-race-challenge-top-senate-democrat)
5. [Michael Katz wins Republican primary for U.S. Senate | News | coasttv.com](https://www.coasttv.com/news/michael-katz-wins-republican-primary-for-u-s-senate/article_8265a288-c56c-4dbb-8bef-e3066c32d418.html)
6. [Who's running in Delaware's federal, Statehouse elections in 2026](https://www.delawareonline.com/story/news/politics/elections/2026/07/15/whos-running-in-delawares-federal-statehouse-elections-in-2026/90899410007/)
7. [John J Whalen III · U.S. House DE-at-large | Amendment](https://www.amendment.app/elections/2026/DE/house/dc83e5e0-3ba0-4230-81f6-732e857399ef/6d3933e9-a3ed-4e31-a70c-788fa0557ab5)
8. [2026 Delaware US Senate Vote History | DDHQ](https://votes.decisiondeskhq.com/races/2026-11-03/delaware-us-senate-general-election/vote-history)
9. [2026 Delaware US Senate Forecast | DDHQ](https://votes.decisiondeskhq.com/races/2026-11-03/delaware-us-senate-general-election/forecast)
10. [September 15, 2026, election results - Ballotpedia](https://ballotpedia.org/September_15,_2026,_election_results)
11. [DE election 2026: Joseph Arminio wins GOP House primary - WHYY](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/)
12. [2026 Delaware US House At-Large Live Election Results | DDHQ](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary)
13. [September 15th, 2026 Delaware Election Results | DDHQ](https://votes.decisiondeskhq.com/elections/2026-09-15/delaware)
14. [https://tldrdailynews.com/news/entertainment/entertainment/no-clear-winner-in-earle-cooper-feud-data-shows-dv1cmhh-ux](https://tldrdailynews.com/news/entertainment/entertainment/no-clear-winner-in-earle-cooper-feud-data-shows-dv1cmhh-ux)
15. [Republican Party primaries in Delaware, 2026 - Ballotpedia](https://ballotpedia.org/Republican_Party_primaries_in_Delaware,_2026)
16. [United States House election in Delaware, 2026 (September 15...](https://ballotpedia.org/United_States_House_election_in_Delaware,_2026_(September_15_Republican_primary))

## Contract Snapshot

For a specific candidate's contract, a "YES" resolution occurs if that candidate is officially declared the Republican nominee for Delaware's At-Large Congressional District following the 2026 primary elections. Conversely, a "NO" resolution occurs if the candidate is not officially declared the nominee. Settlement will be based on these official results, with the maximum payout date set for September 15, 2027.

## Market Discussion

Joseph Arminio secured the Republican nomination for Delaware's at-large U.S. House seat (DE-AL) on September 15, 2026, winning the primary election [[1]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/)[[2]](https://spotlightdelaware.org/2026/09/16/katz-arminio-win-top-gop-nominations-while-atkins-wins-divided-race/)[[3]](https://www.delawarepublic.org/politics-government/2026-09-16/arminio-scores-surprising-win-in-gop-primary-for-u-s-house)[[4]](https://www.wgmd.com/unofficial-results-of-the-delaware-primary-election/). His victory was considered surprising, as he defeated the party-endorsed candidate, Earl Cooper, and previous primary winner John Whalen III [[2]](https://spotlightdelaware.org/2026/09/16/katz-arminio-win-top-gop-nominations-while-atkins-wins-divided-race/)[[3]](https://www.delawarepublic.org/politics-government/2026-09-16/arminio-scores-surprising-win-in-gop-primary-for-u-s-house). Leading up to election day, prediction markets had heavily favored Cooper and Whalen III to win the nomination [[5]](https://kalshi.com/markets/kxdealr/republican-nominee-for-delaware-at-large-congressional-district/kxdealr-26)[[6]](https://robinhood.com/us/en/prediction-markets/elections/events/de-al-republican-nominee-sep-15-2026/)[[7]](https://predictparity.com/markets/k/KXDEALR-26-ECOO).

Sources:

1. [DE election 2026: Joseph Arminio wins GOP House primary - WHYY](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/)
2. [Katz, Arminio win top GOP nominations while Atkins wins divided race - Spotlight Delaware](https://spotlightdelaware.org/2026/09/16/katz-arminio-win-top-gop-nominations-while-atkins-wins-divided-race/)
3. [Arminio scores surprising win in GOP primary for U.S. House | Delaware Public Media](https://www.delawarepublic.org/politics-government/2026-09-16/arminio-scores-surprising-win-in-gop-primary-for-u-s-house)
4. [Unofficial Results of the Delaware Primary Election – WGMD](https://www.wgmd.com/unofficial-results-of-the-delaware-primary-election/)
5. [DE-AL Republican nominee? Odds & Predictions 2026 - Kalshi](https://kalshi.com/markets/kxdealr/republican-nominee-for-delaware-at-large-congressional-district/kxdealr-26)
6. [September 15, 2026: DE-AL Republican nominee Prediction Market](https://robinhood.com/us/en/prediction-markets/elections/events/de-al-republican-nominee-sep-15-2026/)
7. [Will Earl Cooper be the Republican nominee for Delaware's at-large congressional district? | Parity](https://predictparity.com/markets/k/KXDEALR-26-ECOO)

## Market Data

| Contract | Yes Bid | Yes Ask | Last Price | Volume | Open Interest |
| --- | --- | --- | --- | --- | --- |
| Donyale Hall | 0% | 0.1% | 0.1% | 14,662 contracts | 8,031 contracts |
| Earl Cooper | 0% | 0.1% | 0.1% | 32,144 contracts | 22,090 contracts |
| Gavin Solomon | 0% | 0.1% | 0.1% | 1,862 contracts | 1,561 contracts |
| Joseph Arminio | 99% | 100% | 99% | 67,297 contracts | 34,905 contracts |
| John J. Whalen III | 0% | 1% | 1% | 49,435 contracts | 25,518 contracts |
| Lee Murphy | 0% | 0.1% | 0.1% | 19,115 contracts | 9,773 contracts |

## What official results and media calls confirm Joseph Arminio as the winner of the September 15, 2026, DE-AL Republican primary?

Joseph Arminio Reported Votes | 18,559 votes [[1]](https://www.wdel.com/news/joe-arminio-wins-republican-u-s-house-primary-goes-on-to-challenge-rep-mcbride/article_fe437afe-6ccb-567f-bc48-6fdf38711715.html) |
Official Results Status (Sept 16, 2026) | 0% of vote reported [[2]](https://ballotpedia.org/United_States_House_election_in_Delaware,_2026_(September_15_Republican_primary))[[3]](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary)[[4]](https://ballotpedia.org/Joseph_Arminio)[[5]](https://ballotpedia.org/September_15,_2026,_election_results)[[6]](https://newsnation-votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary) |
Race Called By (according to some reports) | Associated Press, NBC News [[1]](https://www.wdel.com/news/joe-arminio-wins-republican-u-s-house-primary-goes-on-to-challenge-rep-mcbride/article_fe437afe-6ccb-567f-bc48-6fdf38711715.html)[[7]](https://www.youtube.com/watch?v=sBKk1qhUMxM)[[8]](https://wtop.com/national/2026/09/joseph-arminio-wins-republican-nomination-for-u-s-house-in-delawares-at-large-congressional-district/) |

**Reports conflict regarding Joseph Arminio's victory in the 2026 DE-AL primary**

Reports conflict regarding Joseph Arminio's victory in the 2026 DE-AL primary. Some sources indicate that Joseph Arminio won the September 15, 2026, Delaware at-large Republican primary, securing 18,559 votes. He reportedly defeated opponents John Whalen, who received 12,471 votes, and Earl Cooper, who garnered 7,723 votes [[1]](https://www.wdel.com/news/joe-arminio-wins-republican-u-s-house-primary-goes-on-to-challenge-rep-mcbride/article_fe437afe-6ccb-567f-bc48-6fdf38711715.html)[[8]](https://wtop.com/national/2026/09/joseph-arminio-wins-republican-nomination-for-u-s-house-in-delawares-at-large-congressional-district/)[[9]](https://www.yahoo.com/news/politics/articles/joseph-arminio-wins-republican-nomination-005545755.html). Major media outlets, including the Associated Press and NBC News, reportedly called the race for Arminio on the night of the primary [[1]](https://www.wdel.com/news/joe-arminio-wins-republican-u-s-house-primary-goes-on-to-challenge-rep-mcbride/article_fe437afe-6ccb-567f-bc48-6fdf38711715.html)[[7]](https://www.youtube.com/watch?v=sBKk1qhUMxM)[[8]](https://wtop.com/national/2026/09/joseph-arminio-wins-republican-nomination-for-u-s-house-in-delawares-at-large-congressional-district/).

Other sources indicate no official confirmation of a winner was available. Conversely, other reports state that as of September 16, 2026, official results or media calls confirming a winner for the September 15, 2026, Delaware At-large Republican primary were not available [[2]](https://ballotpedia.org/United_States_House_election_in_Delaware,_2026_(September_15_Republican_primary))[[3]](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary)[[4]](https://ballotpedia.org/Joseph_Arminio)[[5]](https://ballotpedia.org/September_15,_2026,_election_results)[[6]](https://newsnation-votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary). According to these sources, official election reporting services showed **0%** of the vote reported for the primary [[2]](https://ballotpedia.org/United_States_House_election_in_Delaware,_2026_(September_15_Republican_primary))[[3]](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary)[[4]](https://ballotpedia.org/Joseph_Arminio)[[5]](https://ballotpedia.org/September_15,_2026,_election_results)[[6]](https://newsnation-votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary). Joseph Arminio was confirmed as a candidate in the race [[2]](https://ballotpedia.org/United_States_House_election_in_Delaware,_2026_(September_15_Republican_primary))[[3]](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary)[[4]](https://ballotpedia.org/Joseph_Arminio)[[5]](https://ballotpedia.org/September_15,_2026,_election_results)[[6]](https://newsnation-votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary).

Sources:

1. [Joe Arminio wins Republican U.S. House Primary, goes on... - WDEL](https://www.wdel.com/news/joe-arminio-wins-republican-u-s-house-primary-goes-on-to-challenge-rep-mcbride/article_fe437afe-6ccb-567f-bc48-6fdf38711715.html)
2. [United States House election in Delaware, 2026 (September 15...](https://ballotpedia.org/United_States_House_election_in_Delaware,_2026_(September_15_Republican_primary))
3. [2026 Delaware US House At-Large Live Election Results | DDHQ](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary)
4. [Joseph Arminio - Ballotpedia](https://ballotpedia.org/Joseph_Arminio)
5. [September 15, 2026, election results - Ballotpedia](https://ballotpedia.org/September_15,_2026,_election_results)
6. [2026 Delaware US House At-Large Live Election Results | DDHQ](https://newsnation-votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary)
7. [Joseph Arminio wins Delaware House Republican primary, NBC...](https://www.youtube.com/watch?v=sBKk1qhUMxM)
8. [Joseph Arminio wins Republican nomination for U.S. House... - WTOP](https://wtop.com/national/2026/09/joseph-arminio-wins-republican-nomination-for-u-s-house-in-delawares-at-large-congressional-district/)
9. [Joseph Arminio wins Republican nomination for U.S. House... - Yahoo](https://www.yahoo.com/news/politics/articles/joseph-arminio-wins-republican-nomination-005545755.html)

## How did Joseph Arminio's primary fundraising and key endorsements compare to those of Earl Cooper and John Whalen III?

Joseph Arminio Receipts | $6,634 (as of August 26, 2026) [[1]](https://ballotpedia.org/United_States_House_election_in_Delaware,_2026_(September_15_Republican_primary))[[2]](https://ballotpedia.org/Joseph_Arminio) |
John Whalen III Receipts | $1,589 (as of August 26, 2026) [[1]](https://ballotpedia.org/United_States_House_election_in_Delaware,_2026_(September_15_Republican_primary))[[3]](https://www.fec.gov/data/candidate/H4DE00078/) |
Earl Cooper Endorsement | Officially endorsed by the Delaware Republican Party [[4]](https://timesnewsnetworks.com/republican-upsets-party-backed-rival-to-challenge-first-openly-trans-member-of-congress/)[[5]](https://totalnews.com/republicans-choose-candidate-to-challenge-transgender-member-of-congress-in-november/)[[6]](https://www.delawarepublic.org/politics-government/2026-09-14/voters-head-to-the-polls-tuesday-for-delawares-primary-election) |

**Joseph Arminio led fundraising, though overall campaign totals remained low**

Joseph Arminio led fundraising, though overall campaign totals remained low. In the 2026 Delaware Republican primary, Joseph Arminio surpassed his opponents, Earl Cooper and John Whalen III, in fundraising, despite the modest overall totals for a congressional race [[7]](https://www.predictionedge.com/elections/us-house/delaware-district-at-large-republican-primary/). As of August 26, 2026, Arminio reported **$6,634** in receipts, which was approximately 4.2 times more than Whalen's total and **$6,634** more than Cooper's [[1]](https://ballotpedia.org/United_States_House_election_in_Delaware,_2026_(September_15_Republican_primary))[[2]](https://ballotpedia.org/Joseph_Arminio)[[8]](https://ballotpedia.org/Earl_Cooper_(Delaware))[[3]](https://www.fec.gov/data/candidate/H4DE00078/). John Whalen III reported **$1,589** in receipts by the same date, consisting of **$1,049** in contributions and **$540** in loans [[1]](https://ballotpedia.org/United_States_House_election_in_Delaware,_2026_(September_15_Republican_primary))[[3]](https://www.fec.gov/data/candidate/H4DE00078/). Earl Cooper's campaign-finance table on Ballotpedia showed **$0** in receipts and disbursements, and his retrieved FEC filing did not present a reported fundraising total [[1]](https://ballotpedia.org/United_States_House_election_in_Delaware,_2026_(September_15_Republican_primary))[[8]](https://ballotpedia.org/Earl_Cooper_(Delaware))[[9]](https://docquery.fec.gov/cgi-bin/forms/H4DE01092/1926930/)[[10]](https://www.fec.gov/data/candidate/H4DE01092/).

Ballotpedia identified no endorsements, yet Cooper received party backing. Ballotpedia's research indicated no identified endorsements for Joseph Arminio, Earl Cooper, or John Whalen III in the 2026 Delaware Republican primary, placing all three candidates in a tie for this category [[2]](https://ballotpedia.org/Joseph_Arminio)[[8]](https://ballotpedia.org/Earl_Cooper_(Delaware))[[11]](https://ballotpedia.org/John_Whalen_III_(Delaware)). However, Earl Cooper did receive an official endorsement from the Delaware Republican Party [[4]](https://timesnewsnetworks.com/republican-upsets-party-backed-rival-to-challenge-first-openly-trans-member-of-congress/)[[5]](https://totalnews.com/republicans-choose-candidate-to-challenge-transgender-member-of-congress-in-november/)[[6]](https://www.delawarepublic.org/politics-government/2026-09-14/voters-head-to-the-polls-tuesday-for-delawares-primary-election).

Sources:

1. [United States House election in Delaware, 2026 (September 15 Republican primary) - Ballotpedia](https://ballotpedia.org/United_States_House_election_in_Delaware,_2026_(September_15_Republican_primary))
2. [Joseph Arminio - Ballotpedia](https://ballotpedia.org/Joseph_Arminio)
3. [WHALEN III, JOHN J - Candidate overview | FEC](https://www.fec.gov/data/candidate/H4DE00078/)
4. [Republican upsets party-backed rival to challenge first openly trans member of Congress | Times News Network](https://timesnewsnetworks.com/republican-upsets-party-backed-rival-to-challenge-first-openly-trans-member-of-congress/)
5. [Republicans choose candidate to challenge transgender member of Congress in November - Total News](https://totalnews.com/republicans-choose-candidate-to-challenge-transgender-member-of-congress-in-november/)
6. [Voters head to the polls Tuesday for Delaware's primary election](https://www.delawarepublic.org/politics-government/2026-09-14/voters-head-to-the-polls-tuesday-for-delawares-primary-election)
7. [2026 DE-AL Republican Primary | Polls & Odds](https://www.predictionedge.com/elections/us-house/delaware-district-at-large-republican-primary/)
8. [Earl Cooper (Delaware) - Ballotpedia](https://ballotpedia.org/Earl_Cooper_(Delaware))
9. [FEC Form 2 for Report FEC-1926930](https://docquery.fec.gov/cgi-bin/forms/H4DE01092/1926930/)
10. [COOPER, EARL L - Candidate overview | FEC](https://www.fec.gov/data/candidate/H4DE01092/)
11. [John Whalen III (Delaware) - Ballotpedia](https://ballotpedia.org/John_Whalen_III_(Delaware))

## What key factors or campaign events propelled Joseph Arminio's victory over the field in the September 2026 primary?

Primary Winner | Joseph Arminio (September 15, 2026) [[1]](https://www.foxnews.com/politics/republican-upsets-party-backed-rival-challenge-openly-trans-congress)[[2]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/) |
Seat Won | Delaware's at-large U.S. House seat [[1]](https://www.foxnews.com/politics/republican-upsets-party-backed-rival-challenge-openly-trans-congress)[[2]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/) |
Key Campaign Focus | Economic issues, foreign conflicts, immigration enforcement [[3]](https://whyy.org/articles/election-2026-delaware-primary-congress-republican-candidates/)[[2]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/) |

**Joseph Arminio secured the Republican primary for Delaware's at-large U.S**

Joseph Arminio secured the Republican primary for Delaware's at-large U.S. House seat. He achieved this victory on September 15, 2026, defeating both the party-endorsed candidate, Rev. Earl Cooper, and the 2024 Republican nominee, John Whalen III [[1]](https://www.foxnews.com/politics/republican-upsets-party-backed-rival-challenge-openly-trans-congress)[[2]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/).

Arminio's campaign primarily focused on critical economic concerns for voters. His platform prominently featured an "American Prosperity Plan," which proposed strategies to reduce both public and private debt, and to mitigate the effects of inflation on essential goods and services such as groceries, gasoline, and housing [[3]](https://whyy.org/articles/election-2026-delaware-primary-congress-republican-candidates/)[[2]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/). Beyond economic policy, Arminio also advocated for reducing U.S. involvement in foreign conflicts and strengthening immigration enforcement measures [[3]](https://whyy.org/articles/election-2026-delaware-primary-congress-republican-candidates/)[[2]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/).

Specific campaign events driving Arminio's victory are unstated in the available information. The research does not explicitly detail particular campaign events that led to his success, nor does it establish a direct causal link between his emphasized campaign issues and his triumph over the other primary candidates [[1]](https://www.foxnews.com/politics/republican-upsets-party-backed-rival-challenge-openly-trans-congress)[[2]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/)[[3]](https://whyy.org/articles/election-2026-delaware-primary-congress-republican-candidates/).

Sources:

1. [Republicans select nominee to face trans member of Congress in...](https://www.foxnews.com/politics/republican-upsets-party-backed-rival-challenge-openly-trans-congress)
2. [DE election 2026: Joseph Arminio wins GOP House primary - WHYY](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/)
3. [DE election 2026: Republican primary voter guide for Congress](https://whyy.org/articles/election-2026-delaware-primary-congress-republican-candidates/)

## What were the final certified vote counts and margins for Joseph Arminio and his opponents in the DE-AL Republican primary?

Primary Election Date | September 15, 2026 [[1]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/) |
Joseph Arminio's Partial Lead | 46% (with 33% of vote counted) [[1]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/) |
Final Results Status | Not available as of September 16, 2026 [[1]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/)[[2]](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary)[[3]](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary/vote-history) |

**Joseph Arminio won the 2026 Delaware Republican primary**

Joseph Arminio won the 2026 Delaware Republican primary. He was a candidate in the 2026 Delaware Republican primary for the U.S. House At-Large seat, which was held on September 15, 2026 [[1]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/)[[4]](https://ballotpedia.org/Joseph_Arminio)[[5]](https://ballotpedia.org/United_States_House_election_in_Delaware,_2026_(September_15_Republican_primary))[[6]](https://ballotpedia.org/September_15,_2026,_election_results). On the evening of the primary election, with approximately **33%** of the votes counted, Joseph Arminio was leading with **46%** of the vote. His opponents, John Whalen III and Earl Cooper, received **33%** and **22%** respectively [[1]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/).

Final certified vote counts are not yet publicly available. As of September 16, 2026, the day after the primary election, the final certified vote counts and margins for Joseph Arminio and his opponents are not yet publicly available [[1]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/)[[2]](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary)[[3]](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary/vote-history). The official election data sources do not yet list these final results for the 2026 Delaware U.S. House Republican primary [[2]](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary)[[3]](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary/vote-history).

Sources:

1. [DE election 2026: Joseph Arminio wins GOP House primary - WHYY](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/)
2. [2026 Delaware US House At-Large Live Election Results | DDHQ](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary)
3. [2026 Delaware US House At-Large Vote History | DDHQ](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary/vote-history)
4. [Joseph Arminio - Ballotpedia](https://ballotpedia.org/Joseph_Arminio)
5. [United States House election in Delaware, 2026 (September 15 Republican primary) - Ballotpedia](https://ballotpedia.org/United_States_House_election_in_Delaware,_2026_(September_15_Republican_primary))
6. [September 15, 2026, election results - Ballotpedia](https://ballotpedia.org/September_15,_2026,_election_results)

## What are the initial general election forecasts from outlets like DDHQ for the race between Joseph Arminio and Sarah McBride?

General Election Date | November 3, 2026 [[1]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/)[[2]](https://www.foxnews.com/politics/republican-upsets-party-backed-rival-challenge-openly-trans-congress)[[3]](https://www.wboc.com/elections/joe-arminio-wins-republican-u-s-house-primary-goes-on-to-challenge-rep-mcbride/article_41a388ad-7a07-4745-9755-27e89e1ec6f3.html)[[4]](https://wtop.com/national/2026/09/joseph-arminio-wins-republican-nomination-for-u-s-house-in-delawares-at-large-congressional-district/) |
Republican Primary Winner | Joseph Arminio [[1]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/)[[2]](https://www.foxnews.com/politics/republican-upsets-party-backed-rival-challenge-openly-trans-congress)[[3]](https://www.wboc.com/elections/joe-arminio-wins-republican-u-s-house-primary-goes-on-to-challenge-rep-mcbride/article_41a388ad-7a07-4745-9755-27e89e1ec6f3.html)[[4]](https://wtop.com/national/2026/09/joseph-arminio-wins-republican-nomination-for-u-s-house-in-delawares-at-large-congressional-district/) |
Sarah McBride Prediction Market Probability | around 85% (as of September 16, 2026) [[5]](https://www.coinrithm.com/en/prediction-markets/gemini/delaware-at-large-house-winner) |

**Official general election forecasts from DDHQ are not yet available**

Official general election forecasts from DDHQ are not yet available. As of the current reporting, Decision Desk HQ (DDHQ) records do not yet show initial general election forecasts for the contest between Joseph Arminio and Sarah McBride. The organization states that the Republican primary result is still pending finalization, preventing the issuance of such forecasts at this time [[6]](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary)[[7]](https://integration-votes.decisiondeskhq.com/decision-view/race/293193). Joseph Arminio secured victory in the Republican primary for Delaware's at-large U.S. House seat on September 15, 2026 [[1]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/)[[2]](https://www.foxnews.com/politics/republican-upsets-party-backed-rival-challenge-openly-trans-congress)[[3]](https://www.wboc.com/elections/joe-arminio-wins-republican-u-s-house-primary-goes-on-to-challenge-rep-mcbride/article_41a388ad-7a07-4745-9755-27e89e1ec6f3.html)[[4]](https://wtop.com/national/2026/09/joseph-arminio-wins-republican-nomination-for-u-s-house-in-delawares-at-large-congressional-district/). He is now set to challenge Democratic incumbent Representative Sarah McBride in the general election, scheduled for November 3, 2026 [[1]](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/)[[2]](https://www.foxnews.com/politics/republican-upsets-party-backed-rival-challenge-openly-trans-congress)[[3]](https://www.wboc.com/elections/joe-arminio-wins-republican-u-s-house-primary-goes-on-to-challenge-rep-mcbride/article_41a388ad-7a07-4745-9755-27e89e1ec6f3.html)[[4]](https://wtop.com/national/2026/09/joseph-arminio-wins-republican-nomination-for-u-s-house-in-delawares-at-large-congressional-district/). McBride, for her part, secured her nomination for Delaware's At-Large Congressional District unopposed in the Democratic primary [[8]](https://ballotpedia.org/Sarah_McBride)[[9]](https://ballotpedia.org/United_States_House_election_in_Delaware,_2026_(September_15_Democratic_primary)).

Prediction **market** data suggests a strong advantage for Sarah McBride. As of September 16, 2026, available prediction **market** data for the general election indicates a favorable outcome for incumbent Sarah McBride, showing implied probabilities of victory around **85%** [[5]](https://www.coinrithm.com/en/prediction-markets/gemini/delaware-at-large-house-winner). It is important to note that these figures are derived from prediction markets and do not constitute official general election forecasts from entities such as DDHQ [[5]](https://www.coinrithm.com/en/prediction-markets/gemini/delaware-at-large-house-winner)[[6]](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary)[[7]](https://integration-votes.decisiondeskhq.com/decision-view/race/293193).

Sources:

1. [DE election 2026: Joseph Arminio wins GOP House primary - WHYY](https://whyy.org/articles/election-2026-delaware-primary-us-house-republican-winner/)
2. [Republicans select nominee to face trans member of Congress in November | Fox News](https://www.foxnews.com/politics/republican-upsets-party-backed-rival-challenge-openly-trans-congress)
3. [Joe Arminio wins Republican U.S. House Primary, goes on to challenge Rep. McBride | Elections | wboc.com](https://www.wboc.com/elections/joe-arminio-wins-republican-u-s-house-primary-goes-on-to-challenge-rep-mcbride/article_41a388ad-7a07-4745-9755-27e89e1ec6f3.html)
4. [Joseph Arminio wins Republican nomination for U.S. House in Delaware’s at-large Congressional District – WTOP News](https://wtop.com/national/2026/09/joseph-arminio-wins-republican-nomination-for-u-s-house-in-delawares-at-large-congressional-district/)
5. [Delaware-At-Large House Winner - Gemini Odds | CoinRithm](https://www.coinrithm.com/en/prediction-markets/gemini/delaware-at-large-house-winner)
6. [2026 Delaware US House At-Large Live Election Results | DDHQ](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-house-at-large-republican-primary)
7. [Decision Desk HQ Votes](https://integration-votes.decisiondeskhq.com/decision-view/race/293193)
8. [Sarah McBride - Ballotpedia](https://ballotpedia.org/Sarah_McBride)
9. [United States House election in Delaware, 2026 (September 15...](https://ballotpedia.org/United_States_House_election_in_Delaware,_2026_(September_15_Democratic_primary))

## What Could Change the Odds

**Key catalysts for 2026 U.S.** election prediction markets include presidential approval ratings, economic performance, specifically inflation and unemployment, generic ballot polling, and mid-decade redistricting in states like Ohio, Florida, and California [[1]](https://insidepredictions.com/news/2026-midterm-elections). As of mid-September 2026, some platforms show shifting sentiment toward a possible Democratic Senate edge, while others maintain a slight Republican advantage in retaining the chamber [[1]](https://insidepredictions.com/news/2026-midterm-elections)[[2]](https://www.newsweek.com/democrats-flip-senate-data-shows-12446769)[[3]](https://sweettntmagazine.com/2026-us-midterm-elections-prediction-markets-forecast/).

**The 2026 Delaware primary election for the U.S.** Senate was held on September 15, 2026 [[4]](https://elections.delaware.gov/elections/primary/primary.html)[[5]](https://elections.delaware.gov/public/calendar/pdfs/2026ElectionCalendar.pdf)[[6]](https://news.delaware.gov/2026/09/04/primary-election-tuesday-september-15-2026/)[[7]](https://ballotpedia.org/Delaware_elections,_2026). While some reports indicate Dr. Mike Katz, a physician and former state senator, won the Republican primary on that date, defeating John Shulli to advance to the November 3 general election against Democratic incumbent Chris Coons [[8]](https://whyy.org/articles/election-2026-delaware-primary-senate-republican-winner/)[[9]](https://www.washingtonpost.com/elections/results/2026/09/15/delaware-senate-primary-election-2026-live-results-chris-coons-runs-again/)[[10]](https://www.foxnews.com/politics/gop-anesthesiologist-receives-nod-uphill-race-challenge-top-senate-democrat)[[11]](https://www.coasttv.com/news/michael-katz-wins-republican-primary-for-u-s-senate/article_8265a288-c56c-4dbb-8bef-e3066c32d418.html), authoritative election tracking platforms as of September 16, 2026, reported no official winner or nominee yet announced, with vote counts still to be finalized [[12]](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-senate-republican-primary)[[13]](https://integration-votes.decisiondeskhq.com/races/2026-09-15/delaware-us-senate-republican-primary)[[14]](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-senate-republican-primary/vote-history).

Sources:

1. [2026 Midterm Election Odds: House and Senate Markets](https://insidepredictions.com/news/2026-midterm-elections)
2. [Can Democrats Flip the Senate? What the Data Shows - Newsweek](https://www.newsweek.com/democrats-flip-senate-data-shows-12446769)
3. [2026 US midterm elections: What Metaculus and Robinhood prediction markets are forecasting](https://sweettntmagazine.com/2026-us-midterm-elections-prediction-markets-forecast/)
4. [Primary Election - Department of Elections - State of Delaware](https://elections.delaware.gov/elections/primary/primary.html)
5. [2026 Election Calendar](https://elections.delaware.gov/public/calendar/pdfs/2026ElectionCalendar.pdf)
6. [Primary Election, Tuesday, September 15, 2026 - State of Delaware News](https://news.delaware.gov/2026/09/04/primary-election-tuesday-september-15-2026/)
7. [Delaware elections, 2026 - Ballotpedia](https://ballotpedia.org/Delaware_elections,_2026)
8. [DE election 2026: TK wins GOP Senate primary - WHYY](https://whyy.org/articles/election-2026-delaware-primary-senate-republican-winner/)
9. [Live results: Delaware U.S. Senate primary election 2026](https://www.washingtonpost.com/elections/results/2026/09/15/delaware-senate-primary-election-2026-live-results-chris-coons-runs-again/)
10. [Former Democrat wins GOP US Senate nod in deep-blue Delaware | Fox News](https://www.foxnews.com/politics/gop-anesthesiologist-receives-nod-uphill-race-challenge-top-senate-democrat)
11. [Michael Katz wins Republican primary for U.S. Senate | News | coasttv.com](https://www.coasttv.com/news/michael-katz-wins-republican-primary-for-u-s-senate/article_8265a288-c56c-4dbb-8bef-e3066c32d418.html)
12. [2026 Delaware US Senate Live Election Results | DDHQ](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-senate-republican-primary)
13. [2026 Delaware US Senate Live Election Results | DDHQ](https://integration-votes.decisiondeskhq.com/races/2026-09-15/delaware-us-senate-republican-primary)
14. [2026 Delaware US Senate Vote History | DDHQ](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-senate-republican-primary/vote-history)

## Key Dates & Catalysts

- **Expiration:** September 15, 2027
- **Closes:** September 15, 2027

## Decision-Flipping Events

- Key catalysts for 2026 U.S. election prediction markets include presidential approval ratings, economic performance, specifically inflation and unemployment, generic ballot polling, and mid-decade redistricting in states like Ohio, Florida, and California [[1]](https://insidepredictions.com/news/2026-midterm-elections).
- As of mid-September 2026, some platforms show shifting sentiment toward a possible Democratic Senate edge, while others maintain a slight Republican advantage in retaining the chamber [[1]](https://insidepredictions.com/news/2026-midterm-elections)[[2]](https://www.newsweek.com/democrats-flip-senate-data-shows-12446769)[[3]](https://sweettntmagazine.com/2026-us-midterm-elections-prediction-markets-forecast/).
- The 2026 Delaware primary election for the U.S. Senate was held on September 15, 2026 [[4]](https://elections.delaware.gov/elections/primary/primary.html)[[5]](https://elections.delaware.gov/public/calendar/pdfs/2026ElectionCalendar.pdf)[[6]](https://news.delaware.gov/2026/09/04/primary-election-tuesday-september-15-2026/)[[7]](https://ballotpedia.org/Delaware_elections,_2026).
- While some reports indicate Dr. Mike Katz, a physician and former state senator, won the Republican primary on that date, defeating John Shulli to advance to the November 3 general election against Democratic incumbent Chris Coons [[8]](https://whyy.org/articles/election-2026-delaware-primary-senate-republican-winner/)[[9]](https://www.washingtonpost.com/elections/results/2026/09/15/delaware-senate-primary-election-2026-live-results-chris-coons-runs-again/)[[10]](https://www.foxnews.com/politics/gop-anesthesiologist-receives-nod-uphill-race-challenge-top-senate-democrat)[[11]](https://www.coasttv.com/news/michael-katz-wins-republican-primary-for-u-s-senate/article_8265a288-c56c-4dbb-8bef-e3066c32d418.html), authoritative election tracking platforms as of September 16, 2026, reported no official winner or nominee yet announced, with vote counts still to be finalized [[12]](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-senate-republican-primary)[[13]](https://integration-votes.decisiondeskhq.com/races/2026-09-15/delaware-us-senate-republican-primary)[[14]](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-senate-republican-primary/vote-history).

Sources:

1. [2026 Midterm Election Odds: House and Senate Markets](https://insidepredictions.com/news/2026-midterm-elections)
2. [Can Democrats Flip the Senate? What the Data Shows - Newsweek](https://www.newsweek.com/democrats-flip-senate-data-shows-12446769)
3. [2026 US midterm elections: What Metaculus and Robinhood prediction markets are forecasting](https://sweettntmagazine.com/2026-us-midterm-elections-prediction-markets-forecast/)
4. [Primary Election - Department of Elections - State of Delaware](https://elections.delaware.gov/elections/primary/primary.html)
5. [2026 Election Calendar](https://elections.delaware.gov/public/calendar/pdfs/2026ElectionCalendar.pdf)
6. [Primary Election, Tuesday, September 15, 2026 - State of Delaware News](https://news.delaware.gov/2026/09/04/primary-election-tuesday-september-15-2026/)
7. [Delaware elections, 2026 - Ballotpedia](https://ballotpedia.org/Delaware_elections,_2026)
8. [DE election 2026: TK wins GOP Senate primary - WHYY](https://whyy.org/articles/election-2026-delaware-primary-senate-republican-winner/)
9. [Live results: Delaware U.S. Senate primary election 2026](https://www.washingtonpost.com/elections/results/2026/09/15/delaware-senate-primary-election-2026-live-results-chris-coons-runs-again/)
10. [Former Democrat wins GOP US Senate nod in deep-blue Delaware | Fox News](https://www.foxnews.com/politics/gop-anesthesiologist-receives-nod-uphill-race-challenge-top-senate-democrat)
11. [Michael Katz wins Republican primary for U.S. Senate | News | coasttv.com](https://www.coasttv.com/news/michael-katz-wins-republican-primary-for-u-s-senate/article_8265a288-c56c-4dbb-8bef-e3066c32d418.html)
12. [2026 Delaware US Senate Live Election Results | DDHQ](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-senate-republican-primary)
13. [2026 Delaware US Senate Live Election Results | DDHQ](https://integration-votes.decisiondeskhq.com/races/2026-09-15/delaware-us-senate-republican-primary)
14. [2026 Delaware US Senate Vote History | DDHQ](https://votes.decisiondeskhq.com/races/2026-09-15/delaware-us-senate-republican-primary/vote-history)

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## Historical Resolutions

No historical resolution data available for this series.

## Disclaimer

This content is for informational and educational purposes only and does not constitute financial, investment, legal, or trading advice.
Prediction markets involve risk of loss. Past performance does not guarantee future results.
We are not affiliated with Kalshi or any prediction market platform. Market data may be delayed or incomplete.

### Data Sources & Model Transparency

**Data Sources:** Octagon Deep Research aggregates information from multiple sources including news, filings, and market data.

**Freshness:** Analysis is generated periodically and may not reflect the latest developments. Verify critical information from primary sources.

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