Will at least 5 the Senate Republicans lose re-election in 2026? — 5 or more

- [2026-05-16] Sen. Bill Cassidy (R-LA) finished third in Louisiana's "jungle" primary with 24.8% of the vote, officially losing renomination to Rep. Julia Letlow; this made him the first GOP senator to lose renomination in close to a decade . Source: https://edition.cnn.com/2026/05/17/politics/takeaways-louisiana-senate-primary-bill-cassidy-donald-trump - [2026-05-26] Sen. John Cornyn (R-TX) lost the Republican runoff to Trump-endorsed Attorney General Ken Paxton, receiving about 37% of the vote and becoming the first incumbent Texas senator to lose renomination since 1970 . Source: https://en.wikipedia.org/wiki/John_Cornyn - [2026-05-27] Confirms two incumbent senators—Bill Cassidy of Louisiana and John Cornyn of Texas—lost renomination in their respective primaries , the last time multiple elected incumbents lost renomination being 2010. Source: https://en.wikipedia.org/wiki/2026_United_States_Senate_elections - [2026-07-11] Sen. Lindsey Graham (R-SC), who had already won renomination in the June 9 primary, died suddenly; his sister Darline Graham was appointed and then won a special primary/runoff (Aug 11/25) to be the new GOP nominee. Per the question's rules, death does not count as a "loss," and Darline Graham (appointed after the market's issuance date) is not part of the original Republican cohort tracked by this contract. Source: https://en.wikipedia.org/wiki/2026_United_States_Senate_election_in_South_Carolina - [2026-09-23] Cook Political Report's latest ratings (fetched directly) classify 13 Republican-held seats as Solid/Safe R, 2 Likely R (NE-Ricketts, SC-Graham), 1 Lean R (KS-Marshall), and 5 as Toss-Up: AK-Sullivan, IA-OPEN, ME-Collins, OH-Husted(special), and TX-OPEN (Paxton, the new GOP nominee after Cornyn's primary loss). Of these, only Sullivan, Collins and Husted are incumbents who were part of the original Republican conference and are actively seeking re-election. Source: https://www.cookpolitical.com/ratings/senate-race-ratings - [2026-09-25] Wikipedia's consolidated ratings table (10 forecasters) shows Alaska, Maine, and the Ohio special election consistently rated Toss-Up or worse-than-Toss-Up for Republicans as of late September 2026, with several forecasters (Economist, FiftyPlusOne, Split Ticket) rating them "Lean D (flip)." Source: https://en.wikipedia.org/wiki/2026_United_States_Senate_elections - [2026-09-25] National generic-ballot-style Senate polling averages compiled by Decision Desk HQ, FiftyPlusOne, RealClearPolitics and Silver Bulletin all show Democrats leading by roughly 7.7–8.7 points as of Sept 22–25, 2026, reflecting an unfavorable environment for Republican incumbents. Source: https://en.wikipedia.org/wiki/2026_United_States_Senate_elections - [2026-09-23] Of the 13 Republican incumbents who sought re-election (rather than retiring or facing a primary loss), only Sullivan (AK), Collins (ME) and Husted (OH, appointee) are currently rated as competitive/Toss-Up; the rest (Cotton-AR, Moody-FL, Risch-ID, Hyde-Smith-MS, Marshall-KS, Ricketts-NE, Hagerty-TN, Capito-WV, Rounds-SD) are rated Lean R or stronger. Source: https://en.wikipedia.org/wiki/2026_United_States_Senate_elections - [2026-09-02] The Quorum midterm tracker noted that as of March 2026, major forecasters rate four Senate races as toss-ups: Maine (Susan Collins, R), Michigan (open, Peters retiring, D), North Carolina (open, Tillis retiring, R), and Georgia (Jon Ossoff, D) , showing the competitive landscape has evolved slightly since spring but Maine remained a consistent GOP vulnerability. Source: https://www.quorum.us/blog/2026-midterm-tracker-key-retirements-and-open-seats/ - [2026-09-26] North Carolina (Tillis retiring, open seat) and Texas (Cornyn's old seat, now Paxton) are both rated Lean/Likely D or Toss-Up by multiple forecasters, but neither is relevant to the "5 incumbents lose re-election" count because Tillis retired (doesn't count) and Cornyn's loss is already counted as a primary loss, not a potential second loss in the same seat. Source: https://en.wikipedia.org/wiki/2026_United_States_Senate_elections NOT FOUND: No evidence yet of any additional Senate Republican incumbent losing a primary beyond Cassidy and Cornyn; no general-election results exist yet since Election Day (Nov 3, 2026) has not occurred as of this report's writing (Oct 2, 2026). No official Kalshi-specific count or resolution statement was located (excluded per instructions). BOTTOM LINE: As of October 2, 2026, two sitting Republican senators (Cassidy, Cornyn) have already "lost re-election" via primary defeat, counting toward the ≥5 threshold; reaching 5 requires at least three of the three Republican-held seats currently rated Toss-Up (Alaska-Sullivan, Maine-Collins, Ohio-Husted) to flip in the Nov. 3 general election, a plausible but far-from-certain outcome given a Democratic-leaning national environment and tight forecaster ratings.

- [2026-05-16/05-26] Two sitting Republican senators already lost their primaries this cycle: Bill Cassidy (LA) finished third with 24.8% in the May 16 primary, and John Cornyn (TX) lost the May 26 runoff to Ken Paxton by roughly 27 points. Cornyn is the second sitting U.S. senator to lose a primary this month, following Louisiana Sen. Bill Cassidy, and prior to this year, only two senators had lost primaries in the past 15 years — Lugar and Strange. Under the question's rules (primary losses count), this is already 2 of the 5 needed. - [2026-09-30] Wikipedia's tracker (compiling Cook, DDHQ, Economist, FPO, Fox, Inside Elections, RCP, Sabato, Silver Bulletin, Split Ticket) confirms two incumbent senators—Bill Cassidy of Louisiana and John Cornyn of Texas—lost renomination in their respective primaries, the first time an elected incumbent lost renomination since Richard Lugar in 2012 — an extremely rare base-rate event historically. - [2022-ish historical] Between 1946 and 2012, only 5 percent of incumbent senators… lost their party primaries , underscoring how unusual 2026's two primary losses already are relative to the historical base rate. - [2026-09-23] Cook Political Report's current ratings list seven Senate seats as toss-ups, five of them Republican-held: AK Sullivan, IA OPEN, ME Collins, MI OPEN, NH OPEN, OH Husted, TX OPEN (IA, MI, NH, TX are now open seats without an incumbent GOP candidate since Ernst/Peters/Shaheen retired and Cornyn lost his primary). - [2026-09-23] There are six Republican-held Senate seats rated by Cook as a "Toss Up" or better for Democrats. Georgia, Kansas and South Carolina all shifted toward Democrats in late-September Cook updates amid a deteriorating environment for the GOP. - [2026-09-25] Aggregated generic-ballot/Senate polling trackers compiled on Wikipedia (DDHQ, FiftyPlusOne, RealClearPolitics, Silver Bulletin) show Democrats ahead by a consistent margin: Democrats +8.2% on average as of Sept 22-25, 2026. - [2026-09-25 multi-source table] Among incumbent Republicans still actually seeking re-election in competitive seats, multiple forecasters (Economist, FPO, Silver Bulletin) rate Alaska (Sullivan), Maine (Collins), and Ohio special (Husted) as "Lean D (flip)" rather than toss-up, while Kansas (Marshall) sits at "Lean R," Nebraska (Ricketts) mostly "Likely R" (Sabato: Tossup), and South Carolina (appointed incumbent Graham) "Likely R"/"Lean R." - [2026-10-02] Historically, Senate incumbent reelection rates are high but more variable than the House — in the Senate, there is only slightly more variation, given the statewide nature of the race, but it is still a very high majority of incumbents who win reelection — and following the "Reagan revolution" that swept Republicans into office in 1980, Democrats have been defeated at only half the rate of Republicans (8% vs. 16%) in incumbent Senate races, i.e., GOP incumbents have historically lost general elections at roughly double the rate Democratic incumbents have, though a 16% incumbent-loss rate still implies that even in a bad GOP year, a 5-of-~13 non-retired-incumbent loss rate (~38%) would be well above historical norms absent a true wave. - [2026-09-30] Roll Call's "most vulnerable senators" tracker a month before Election Day confirms Cassidy and Cornyn "fall off" the list because they already lost their primaries, leaving the general-election battle concentrated in the toss-up seats listed above. - [2026-10-02] To reach "5 or more" GOP losses, 2 are already locked in (Cassidy, Cornyn primary losses); the remaining 3 would have to come from actual November general-election defeats of sitting/appointed GOP incumbents still on the ballot — realistically Sullivan (AK), Collins (ME), Husted (OH), with Marshall (KS), Ricketts (NE) or Graham (SC) as lower-probability additional losses, since open-seat losses (Iowa, North Carolina, New Hampshire, Michigan) do not count under the question's "actively sought re-election" rule. BOTTOM LINE: The reference class for "5+ Senate incumbents of one party losing re-election in a cycle" is historically rare (last comparable scale of incumbent losses was the 2006/2008 Democratic wave years), but 2026 is already unusual: two GOP incumbents (Cassidy, Cornyn) have already lost via primary, an outcome essentially unprecedented in the post-2012 era, and current nonpartisan ratings plus polling (Dem +8 generic ballot) put 3+ more sitting GOP incumbents (Sullivan, Collins, Husted, and possibly Marshall/Ricketts/Graham) in toss-up or lean-Democrat territory heading into November — making the base rate for this specific cycle meaningfully elevated versus long-run historical norms, even though hitting exactly 5+ still requires an unusually bad GOP November. NOT FOUND: A specific consolidated betting-market or forecaster probability estimate for "exactly how many Republican Senate incumbents lose in November 2026" (seat-count distributions from Silver Bulletin/Economist models beyond the lean/toss-up labels) was not located; also could not confirm any additional GOP primary losses beyond Cassidy and Cornyn as of October 2, 2026.

YES means: five or more sitting Senate Republicans who actively sought re-election in 2026 end up losing their bid (via primary, runoff, or general election) under the contract's counting rules. - [2026-10-02] Two GOP incumbents are already locked in as losses: Bill Cassidy (LA) and John Cornyn (TX) both lost renomination in their primaries, an outcome Wikipedia's consolidated tracker calls the first time an elected incumbent senator lost renomination since Richard Lugar in 2012, and the first time two did so since 2010. https://en.wikipedia.org/wiki/2026_United_States_Senate_elections - [2026-10-02] Polymarket's dedicated sibling market "Will the Republican Party hold 47 or fewer Senate seats after the 2026 midterm elections?" — equivalent to a net loss of 6+ seats from the current 53 — was priced at 39% on the Polymarket Senate hub, indicating traders see a GOP seat-loss scale compatible with ≥5 individual incumbent defeats as a live, non-trivial scenario. https://polymarket.com/politics/senate-elections - [2026-10-01] In Alaska, Polymarket/RCP aggregation shows Democrat Mary Peltola favored over incumbent Dan Sullivan, with the RCP average reading "Peltola +2.3" and Polymarket pricing Peltola around 71% to win. https://www.realclearpolling.com/polls/senate/general/2026/alaska/peltola-vs-sullivan - [2026-10-01] In Ohio's special election, back-to-back late polls (Suffolk/USA Today and Marist, both released Oct 1) show Sherrod Brown leading appointed incumbent Jon Husted by 3 and 8 points respectively, continuing "a run of public polling that has generally shown Brown competitive with or leading Husted." https://www.nbc4i.com/news/your-local-election-hq/two-ohio-polls-show-sherrod-brown-leading-jon-husted-in-u-s-senate-race/ - [2026-10-01] In Maine, independent trackers are split but tight: FiftyPlusOne's adjusted average on Oct 1 had Jackson +2 (47.8%–45.6%), while a new NYT/Siena poll (Sept 15–22) and an InsiderAdvantage poll (Sept 22–23) showed Collins narrowly ahead or tied, underscoring the race remains a true toss-up a month out. https://fiftyplusone.news/polls/senate/general/maine - [2026-10-02] Kansas — previously seen as only "Lean R" — has newly entered toss-up territory: Wikipedia's Sept 22–26 forecaster compilation shows both the Economist and RealClearPolitics now rating Marshall vs. Hamilton a "Tossup," and PollingSource's weekly average (through Sept 24) has Democrat Adam Hamilton leading Marshall 50%–48%. https://en.wikipedia.org/wiki/2026_United_States_Senate_elections - [2026-09-18] An Emerson College/Hill poll (Sept 16–18) found Democrat Adam Hamilton leading Marshall 45%–43% in Kansas, a state that "has not elected a Democrat to the Senate since 1932," showing the erosion in a seat once considered safe. https://www.ksn.com/news/your-local-election-hq/new-kansas-senate-poll-shows-tight-race-between-hamilton-and-marshall/ - [2026-09-25] Nationwide, four major Senate polling averages (DDHQ, FiftyPlusOne, RealClearPolitics, Silver Bulletin) converge on Democrats +7.7 to +8.7 points as of Sept 22–25, an unusually large generic-ballot gap that, combined with Trump's "unpopularity amidst the 2026 Iran war," is cited by Wikipedia's editors as improving Democratic chances in Alaska, Ohio, Texas and North Carolina simultaneously. https://en.wikipedia.org/wiki/2026_United_States_Senate_elections - [2026-10-02] The consolidated 10-forecaster "Overall" row on Wikipedia's tracker (Sept 17–26 dates) shows a range of only 45–50 solid/likely/safe Republican seats out of 47 non-tossup calls, with Republicans' floor falling as low as 45 in RCP's model and tossups reaching as many as 9 (RCP) — meaning several independent models already price in GOP losing more Class 2 seats than needed to hit the ≥5 threshold when combined with the two already-realized primary losses. https://en.wikipedia.org/wiki/2026_United_States_Senate_elections - [2026-09-23] Coinspeaker's report on Polymarket's Senate-control market (63% Democratic, $5.4M volume) noted "Republican-aligned selections held stronger positions elsewhere" but still flagged Alaska, Maine, Ohio and Texas as the specific drivers of the Democratic price, confirming market-based consensus that at least 3–4 Republican-held seats are genuinely contestable beyond Cassidy/Cornyn. https://coinspeaker.com/midterm-prediction-market-odds-polymarket-2026-senate BOTTOM LINE: With 2 of 5 needed losses already locked in via primary defeats, the YES path requires only 3 of 4 realistically competitive Republican-held seats (Alaska-Sullivan, Maine-Collins, Ohio-Husted, and now Kansas-Marshall) to flip in November; current polling averages, forecaster tossup ratings, and Polymarket pricing (Peltola ~71%, Brown ~58-60%, Jackson ~57%, and a newly tightening Kansas race) all show this as a plausible, not merely speculative, outcome in a Democratic-leaning national environment (D+8 generic ballot). NOT FOUND: No seat-by-seat Polymarket or Kalshi market specifically tracking "exact count of GOP incumbents losing re-election"; could not confirm any additional GOP primary losses beyond Cassidy and Cornyn; no post-October polling yet for Nebraska (Ricketts) or South Carolina (Graham) beyond the already-cited Likely/Lean R ratings.

YES means: five or more Republican senators who actively sought re-election in 2026 fail to win (via primary, runoff, or general election), counting toward the ≥5 threshold under the contract's rules. - [2026-10-01] Prediction markets price the "undecided" GOP toss-up seats well short of certain losses: Kalshi's own Alaska market shows Dan Sullivan at 32% to win, not nearly 0%, implying real residual odds Republicans hold that seat. Source: https://kalshi.com/markets/senateak/alaska-senate-race/senateak-26 - [2026-10-01] In Kansas, despite alarming public polls showing Democrat Adam Hamilton tied or slightly ahead of Roger Marshall, Kalshi's own market prices Marshall at 69-71% to win, and Polymarket-style trackers show Nebraska's Ricketts at roughly 70-71% — both far from the kind of near-certain Democratic flip needed to push the GOP loss count to 5 or beyond. Source: https://kalshi.com/markets/senateks/kansas-senate-race/senateks-26; https://defirate.com/news/iowa-kansas-nebraska-senate-prediction-markets/ - [2026-10-01] Maine has visibly tightened in Collins' favor in the final month: the NYT/Portland Press Herald/Siena poll (Sept 15-22) gave the five-term Republican incumbent ahead of Jackson for the first time, 49% to 46% , and a subsequent co/efficient poll gave her another edge, with Newsweek noting Jackson has edged out the five-term senator in nearly every survey until this reversal. This is the opposite direction from "building toward a GOP loss." - [2026-10-01] Collins has a documented, large history of outrunning her polling: in 2020 she trailed in every public poll (down as much as 6.5 points in the RCP average) yet won by 8.6 points, and multiple 2026 analysts explicitly flag this pattern is recurring, with Collins "currently polling worse against Platner" early on but still gaining late, per Newsweek's direct comparison of 2020 vs 2026 polling trendlines. Source: https://www.newsweek.com/susan-collins-polls-numbers-worse-than-in-2020-can-she-defy-odds-again-12003873; https://www.newsweek.com/susan-collins-blasted-by-troy-jackson-over-fbi-probe-reportcorruption-12474119 - [2026-10-01] Ohio's special election, the third "must-flip" seat for YES, remains within single digits: RealClearPolitics' poll average (through early Oct) shows RCP Average Brown +3.1, 46.9% to 43.8% , and even the pro-Brown Suffolk/USA Today poll put Brown with roughly 47% support among likely voters, compared with 44% for Husted, falling within the poll's margin of error — not a decisive, locked-in Democratic win. - [2026-10-01] Ohio also shows genuine within-party uncertainty from methodology: a Marist poll had Brown up 8 among registered voters, but voters narrowly expected Brown to win, with 50% predicting his victory and 47% choosing Husted — marking a reversal from a recent Bowling Green State University poll, in which 53% expected Husted to win despite Brown's lead , indicating the race remains genuinely contested rather than settled. - [2026-10-01] Even in the worst-polling scenario, reaching 5 GOP losses requires Sullivan, Collins, and Husted to all lose AND at least one of Marshall (KS) or Ricketts (NE) to also lose; but Nebraska's independent-vs-incumbent dynamic (Osborn), while drawing attention, still has Ricketts favored in markets at ~70%, and Kansas Marshall, despite one Democratic-leaning poll, still polls competitively in Emerson's data (45-43, within MoE) and leads on Kalshi's own market by a wide margin — meaning the "extra" losses beyond the three headline toss-ups are not well-supported by current data. Source: https://emersoncollegepolling.com/kansas-2026/; https://defirate.com/news/iowa-kansas-nebraska-senate-prediction-markets/ - [2026-10-01] Historically, achieving 3 incumbent general-election losses in one toss-up tier, let alone 5 total including primary losses, is rare; Roll Call's tracker (cited in prior research) already treats Cassidy and Cornyn as "off the board," meaning the market's resolution now hinges entirely on whether Republicans can hold at least one of Alaska/Maine/Ohio plus both Kansas and Nebraska — a compound condition requiring Republicans to lose virtually every competitive race simultaneously, which polling aggregation (margin-of-error toss-ups, not blowout leads) does not currently support. - [2026-10-01] Split-ticket and crossover patterns that have historically saved Republican incumbents in blue-leaning states remain visible in 2026: the NYT/Siena Maine poll found she won a whopping 12% of voters who backed Democrat Kamala Harris in 2024, while Jackson got only 3% of Trump voters , suggesting the kind of personal-brand resilience that has repeatedly defied modeled "wave" expectations in close Senate races. BOTTOM LINE: With only two losses (Cassidy, Cornyn) currently locked in, reaching the 5-loss threshold requires nearly all three toss-up incumbents (Sullivan-AK, Collins-ME, Husted-OH) to lose AND at least one additional "Likely/Lean R" incumbent (Marshall-KS or Ricketts-NE) to also fall — a compounding, multi-race requirement that current polling-average margins (low single digits, within MoE) and prediction markets (pricing each GOP incumbent at 30-70% to survive, not near-zero) do not support as the modal outcome, especially given Collins' historical pattern of outperforming polls and recent late-race tightening in her favor. NOT FOUND: No seat-by-seat joint-probability model (e.g., from Silver Bulletin or Decision Desk HQ) estimating P(5+ GOP incumbent losses) specifically was located; also could not confirm any post-October 1 polling for South Carolina (Graham) or Iowa/open seats relevant to a hypothetical sixth loss scenario.