# How many Senate Republicans will lose their primary in 2026? Before Nov 3, 2026 Updated: April 29, 2026 Category: Elections Tags: Primaries HTML: /markets/elections/primaries/how-many-senate-republicans-will-lose-their-primary-in-2026/ ## Short Answer **Key takeaway.** Both the **model** and the **market** expect 2 Senate Republicans to lose their primary in 2026, with no compelling evidence of mispricing. ## Key Claims (January 2026) **- - Donald Trump anti-endorsed Senator Cassidy, backing an A-tier challenger.** - Texas AG Ken Paxton declared an A-tier primary challenge against Senator Cornyn. - Louisiana GOP is considering withholding endorsement for Senator Bill Cassidy. - Incumbency provides significant advantage, even with formidable primary threats. - Senator Cornyn maintains a substantial defensive primary war chest. ### Why This Matters (GEO) - AI agents extract claims, not arguments. - Improves citation probability in summaries and answer cards. - Enables fact stitching across multiple sources. ## Executive Verdict **Key takeaway.** **Model**'s **4.8%** for zero losses is 2.2pp below **market**'s 7c, despite strong primary challenges making it improbable. ### Who Wins and Why | Outcome | Market | Model | Why | | --- | --- | --- | --- | | 4 or more | 12.0% | 11.3% | Market higher by 0.7pp | | 2 | 41.0% | 38.7% | Market higher by 2.3pp | | 3 | 12.0% | 11.3% | Market higher by 0.7pp | ## Model vs Market | Outcome | Market Probability | Octagon Model Probability | | --- | --- | --- | | 4 or more | 12.0% | 11.3% | | 2 | 41.0% | 38.7% | | 3 | 12.0% | 11.3% | | 1 | 29.0% | 33.7% | | 0 | 7.0% | 4.8% | - Expiration: November 3, 2026 ## Market Behavior & Price Dynamics This prediction market has exhibited a sideways trading pattern, with the probability of one or more Senate Republican primary losses in 2026 confined to a narrow range between 2.0% and 7.0%. The market opened at 6.0% and is currently trading at 7.0%, the high end of its historical range. This 7.0% level appears to be acting as a point of resistance, while the low of 2.0% has served as a support level. Given the lack of specific news or external context, the fluctuations within this band, such as the drop to 3.0% and the subsequent rise to 7.0%, cannot be attributed to any specific event and likely reflect internal market dynamics or low-volume trades. The total traded volume of 3,322 contracts over the market's history, combined with sample data points showing zero volume, suggests that trading activity has been inconsistent and generally low. This pattern of low volume indicates a lack of strong conviction from market participants. While the price is currently testing its all-time high, the absence of significant trading volume behind this move suggests it may not be a high-conviction breakout. Overall, the chart reflects a market sentiment that consistently views the likelihood of a Senate Republican incumbent losing a primary as very low. The stable, sideways movement within the tight 2.0% to 7.0% band indicates a stable consensus among traders. The market has not priced in any significant event or candidate vulnerability that would drastically alter this low-probability outlook. ## Significant Price Movements #### 📈 April 26, 2026: 8.8pp spike Price increased from 3.2% to 12.0% **Outcome:** 3 **What happened:** No supporting research available for this anomaly. #### 📈 April 19, 2026: 11.0pp spike Price increased from 1.0% to 12.0% **Outcome:** 3 **What happened:** No supporting research available for this anomaly. ## Contract Snapshot Here's a summary of the contract rules for this specific Kalshi market: 1. **YES resolution**: This market resolves to "Yes" if exactly two Republican Senate members lose their primary election in 2026 before November 3, 2026. 2. **NO resolution**: It resolves to "No" if the number of Republican Senate members who lose their primary in 2026 before November 3, 2026, is not exactly two. 3. **Key dates/deadlines**: The market opens on January 23, 2026, at 4:00 PM EST and will close by November 3, 2026, at 10:00 AM EST, or earlier if the outcome is mathematically guaranteed. Projected payouts occur 30 minutes after closing. 4. **Special settlement conditions**: Only incumbent Republican Senators seeking re-election to the same legislative body are included if they lose their primary to another candidate, excluding "top-two" primaries where they advance. Resolution relies on information from various major news sources and the Federal Register, and individuals employed by these source agencies are prohibited from trading this contract. ## Market Discussion The market discussion primarily focuses on the expected low number of Republican Senate primary losses in 2026, with a strong consensus among several traders that higher numbers (3+) are overestimated due to confusion with general election outcomes. Many believe the true number of losses will be very low, likely 0, 1, or 2. Arguments for a low outcome include the inherent difficulty of unseating incumbents in primaries and strategic considerations around endorsements in specific races like Texas. ## Market Data | Contract | Yes Bid | Yes Ask | Last Price | Volume | Open Interest | | --- | --- | --- | --- | --- | --- | | 0 | 2.1% | 7% | 7% | $37,693.62 | $22,249.44 | | 1 | 29% | 30% | 29% | $54,790.94 | $32,243.61 | | 2 | 40% | 41% | 41% | $72,322.32 | $35,094.62 | | 3 | 7.1% | 12% | 12% | $58,503.72 | $35,538.55 | | 4 or more | 10% | 12% | 12% | $118,953.36 | $67,600.48 | ## Which Senators Did Trump Anti-Endorse Before 2026 Primary Deadlines? Bill Cassidy Anti-Endorsement | Yes, Trump backed primary challenger Julia Letlow in early 2026 [[^]](https://www.wsls.com/news/politics/2026/01/20/after-trump-endorsement-rep-julia-letlow-launches-primary-against-sen-bill-cassidy-in-louisiana/). | John Cornyn Anti-Endorsement | No, Trump stayed out of the Texas Senate primary despite earlier vows [[^]](https://www.nbcnews.com/politics/2026-election/trump-endorse-soon-texas-republican-senate-primary-cornyn-paxton-rcna261566). | Lindsey Graham Anti-Endorsement | No information available in provided sources [[^]](https://www.wsls.com/news/politics/2026/01/20/after-trump-endorsement-rep-julia-letlow-launches-primary-against-sen-bill-cassidy-in-louisiana/). | **Donald Trump issued an anti-endorsement against Senator Bill Cassidy** Donald Trump issued an anti-endorsement against Senator Bill Cassidy. In early 2026, Trump publicly backed Representative Julia Letlow's primary challenge to Senator Cassidy, prompting Letlow to launch her campaign [[^]](https://www.wsls.com/news/politics/2026/01/20/after-trump-endorsement-rep-julia-letlow-launches-primary-against-sen-bill-cassidy-in-louisiana/). Media outlets characterized Trump's move as "knifing" Senator Cassidy by supporting a potential primary opponent. These events occurred around January 2026, preceding Louisiana's 2026 primary qualifying deadline [[^]](https://trib.al/9QHxhED). Conversely, Donald Trump did not anti-endorse Senator John Cornyn or Lindsey Graham. Trump initially stated in early 2026 that he would endorse "soon" in the Texas Senate primary but ultimately refrained from endorsing in either the primary or runoff elections [[^]](https://www.nbcnews.com/politics/2026-election/trump-endorse-soon-texas-republican-senate-primary-cornyn-paxton-rcna261566). For Senator Lindsey Graham, the available research contains no information regarding any direct negative mention or "anti-endorsement" from Donald Trump before South Carolina's 2026 primary filing deadline. ## Which GOP Incumbents Faced $2M+ Primary Spending from Key PACs? Targeted GOP Incumbents (>$2M opposition) | Not identified in provided research [[^]](https://www.fec.gov/data/committee/C00487470/) | Club for Growth Action primary involvement | Known for involvement in Republican primaries and FEC disclosures [[^]](https://www.fec.gov/data/committee/C00487470/) | Senate Conservatives Fund primary support | Supports conservative candidates [[^]](https://www.senateconservatives.com/%23candidates) | **Specific data on anti-establishment PAC spending is unavailable from current sources** Specific data on anti-establishment PAC spending is unavailable from current sources. The provided web research results do not contain the specific, granular independent expenditure data from Club for Growth Action or Senate Conservatives Fund necessary to identify GOP incumbents targeted with more than **$2** million in combined independent expenditures during the two quarters preceding their state's primary [[^]](https://www.fec.gov/data/committee/C00487470/). While both Club for Growth Action and Senate Conservatives Fund are recognized for their involvement in Republican primaries and their support for conservative candidates, the existing documentation does not offer a summary or detailed breakdown of independent expenditures specifically directed against GOP incumbents totaling over **$2** million within the designated timeframe [[^]](https://www.fec.gov/data/committee/C00487470/). Available information primarily details endorsements, not specific opposition spending by these PACs. Many of the sources refer to the political action committees' endorsements rather than providing detailed information about opposition spending [[^]](https://www.senateconservatives.com/%23candidates). Furthermore, news articles discuss substantial overall outside spending in various Republican primaries, such as those in Kentucky and Texas, but these discussions focus on total spending by broader "outside groups" or "dark money" [[^]](https://www.weku.org/the-commonwealth/2026-04-20/billionaires-dark-money-bankroll-much-of-48m-spent-in-kentucky-gop-senate-primary). These reports do not attribute specific independent expenditure amounts from Club for Growth Action or Senate Conservatives Fund against particular GOP incumbents that surpass the **$2** million threshold for the specified period. Consequently, based on the provided sources, specific GOP incumbents meeting these outlined criteria cannot be identified [[^]](https://www.weku.org/the-commonwealth/2026-04-20/billionaires-dark-money-bankroll-much-of-48m-spent-in-kentucky-gop-senate-primary). ## What Actions Did State GOPs Take Against Incumbent Senators in 2025? Texas Censure Status | Senator John Cornyn censured by April 2025, along with five other individuals on October 11, 2025 [[^]](https://texasgop.org/wp-content/uploads/2025/09/Censure-Resolutions-for-Consideration-on-October-11.pdf). | Texas Ballot Restriction | Effort to ban censured individuals from primary ballot rejected in 2025 [[^]](https://www.texastribune.org/2025/10/11/texas-gop-srec-censure/). | Louisiana Endorsement Status | Louisiana GOP considering withholding endorsement from Senator Bill Cassidy as of August 2025 [[^]](https://shreveporttimes.com/story/news/2025/08/12/will-louisiana-republican-party-withhold-endorse-of-bill-cassidy-because-of-trump-impeachment-vote/85618783007). | **Texas Republicans passed multiple censure resolutions, but rejected blocking incumbents from ballots** Texas Republicans passed multiple censure resolutions, but rejected blocking incumbents from ballots. Senator John Cornyn was censured by April 2025, stemming from his support for a gun safety bill [[^]](https://www.texastribune.org/2025/04/01/john-cornyn-texas-republican-party-abraham-george/). Furthermore, on October 11, 2025, the Republican Party of Texas passed censure resolutions against five other individuals [[^]](https://texasgop.org/wp-content/uploads/2025/09/Censure-Resolutions-for-Consideration-on-October-11.pdf). While the state party had earlier in 2025 considered a bid to block censured members from the primary ballot [[^]](https://www.texastribune.org/2025/08/11/texas-gop-republican-party-censures-primary-ballot-dustin-burrows/), this effort was ultimately rejected by the Texas GOP [[^]](https://www.texastribune.org/2025/10/11/texas-gop-srec-censure/). Consequently, although censures took place, the specific mechanism to formally shift the state party apparatus to a challenger by blocking an incumbent from the ballot was not adopted in 2025. Louisiana considered withholding endorsement, while South Carolina showed no similar action. In Louisiana, the Republican Party is actively considering whether to withhold its endorsement from Senator Bill Cassidy for his upcoming Senate race, a decision being evaluated as of August 2025 [[^]](https://shreveporttimes.com/story/news/2025/08/12/will-louisiana-republican-party-withhold-endorse-of-bill-cassidy-because-of-trump-impeachment-vote/85618783007). This consideration follows his earlier censure by the party in February 2021 for his vote to convict former President Donald Trump [[^]](https://apnews.com/article/donald-trump-censures-bill-cassidy-impeachments-trump-impeachment-76bdbd322bcc1e1a6af1919a66f66505). Such an action, if taken, would represent a formal shift of the state party apparatus away from the incumbent senator. Conversely, research indicates no state Republican Party organizations in South Carolina passed an official resolution of 'censure' or 'no **confidence**' against an incumbent senator during their 2025 or early 2026 party conventions that would signal a formal shift to a challenger [[^]](https://www.postandcourier.com/greenville/politics/greenville-county-gop-pamela-evette-censure/article_3f164938-fba7-46c0-b8a9-bd6818091f9e.html). ## Did Republican Senators Successfully Build Q4 2025 Defensive War Chests? Susan Collins Cash on Hand | $10.1 million (Q4 2025) [[^]](https://docquery.fec.gov/cgi-bin/forms/C00314575/1943203/) | Thom Tillis Cash on Hand | $5.6 million (Q4 2025) [[^]](https://www.ellisinsight.com/senate/senate-cash/) | John Cornyn Cash on Hand | $12.3 million (Q4 2025) [[^]](https://www.ellisinsight.com/senate/senate-cash/) | **Senator Susan Collins successfully established a strong defensive financial position** Senator Susan Collins successfully established a strong defensive financial position. She concluded Q4 2025 with a substantial **$10,135,165.74** cash on hand [[^]](https://docquery.fec.gov/cgi-bin/forms/C00314575/1943203/). As of the Q4 2025 FEC filing deadline, publicly available sources did not list any declared primary challengers for Senator Collins [[^]](https://www.ellisinsight.com/senate/senate-cash/). Consequently, without a declared challenger to compare against, her war chest inherently exceeded the 10-times threshold relative to any non-existent declared opponent's Q4 2025 cash-on-hand total. Senators Tillis and Cornyn similarly established strong financial deterrents. Senator Thom Tillis reported **$5.6** million cash on hand at the close of Q4 2025 [[^]](https://www.ellisinsight.com/senate/senate-cash/). Research for the same period revealed no declared primary challengers for Senator Tillis [[^]](https://www.ellisinsight.com/senate/senate-cash/), meaning he successfully met the specified financial benchmark. Likewise, Senator John Cornyn ended Q4 2025 with a significant **$12.3** million cash on hand [[^]](https://www.ellisinsight.com/senate/senate-cash/). While some potential challengers, such as Attorney General Ken Paxton and U.S. Rep. Chip Roy, were mentioned as actively fundraising, sources explicitly stated that neither had "officially declared their candidacies" by the Q4 2025 deadline [[^]](https://www.texastribune.org/2026/01/31/texas-senate-gop-primary-fundraising-q4-cornyn-paxton-hunt-2026/). Given the criteria of comparing against a declared primary challenger, Senator Cornyn, like Collins and Tillis, had no officially declared primary opposition with reported Q4 2025 fundraising to measure against, thus fulfilling the requirement for building a defensive 'war chest' by this metric. ## Has an A-Tier Challenger Declared Against a GOP Senate Incumbent? A-Tier Challenger Status | Yes, for the 2026 election [[^]](https://www.reuters.com/world/us/republican-texas-attorney-general-paxton-challenge-senator-cornyn-primary-2025-04-09/) | Declared Challenger | Texas Attorney General Ken Paxton [[^]](https://www.reuters.com/world/us/republican-texas-attorney-general-paxton-challenge-senator-cornyn-primary-2025-04-09/) | Incumbent Challenged | Senator John Cornyn (Texas) [[^]](https://ballotpedia.org/United_States_Senate_election_in_Texas,_2026) | **At least one "A-tier" challenger has officially declared a primary campaign against a GOP Senate incumbent** At least one "A-tier" challenger has officially declared a primary campaign against a GOP Senate incumbent. Texas Attorney General Ken Paxton, who is a current statewide officeholder and thus meets the "A-tier" definition for this finding, has announced his challenge against incumbent Republican Senator John Cornyn in the 2026 Republican primary [[^]](https://www.reuters.com/world/us/republican-texas-attorney-general-paxton-challenge-senator-cornyn-primary-2025-04-09/). Senator Cornyn is the incumbent for the 2026 United States Senate election in Texas [[^]](https://ballotpedia.org/United_States_Senate_election_in_Texas,_2026). Other challengers do not meet the "A-tier" criteria as defined. For example, Alabama Attorney General Steve Marshall has officially entered a U.S. Senate race, but available sources do not specify it as a primary challenge against a GOP Senate incumbent [[^]](http://www.abc3340.com/news/local/alabama-ag-steve-marshall-officially-enters-us-senate-race-vows-conservative-leadership). Additionally, in West Virginia, State Senator Tom Willis has filed a GOP primary challenge against incumbent Senator Shelley Moore Capito; however, a state senator does not fall under the "A-tier" definition of a current statewide officeholder [[^]](https://mountaineerjournal.com/2026/01/17/state-sen-tom-willis-files-gop-primary-challenge-against-capito-in-u-s-senate-race/). ## What Could Change the Odds **Key takeaway.** Catalyst analysis unavailable. ## Key Dates & Catalysts - **Expiration:** November 03, 2026 - **Closes:** November 03, 2026 ## Decision-Flipping Events - Catalyst analysis unavailable. ## Related Research Reports - [EU loses a member before 2030?](/markets/elections/international/eu-loses-a-member-before-2030/) - [Who will run for the 2028 Republican presidential nomination?](/markets/elections/2028/who-will-run-for-the-2028-republican-presidential-nomination/) - [How many AIPAC-endorsed candidates will lose their primaries?](/markets/elections/how-many-aipac-endorsed-candidates-will-lose-their-primaries/) - [Alaska Senate winner? (Person)](/markets/elections/us-elections/alaska-senate-winner-person/) ## 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.