Texas Republican Senate Runoff: Margin of Victory
Short Answer
Both the model and the market overwhelmingly agree that Ken Paxton won the Texas Republican Senate Runoff by a margin of 20% or more, with only minor residual uncertainty.
1. Executive Verdict
- Ken Paxton defeated John Cornyn by 25-28 percentage points.
- Official results confirmed Ken Paxton's margin above 20%.
- John Cornyn significantly outspent Ken Paxton 17-to-1 in advertising.
- An April 2026 poll showed Paxton leading by only three points.
- President Trump's late endorsement reportedly shifted runoff momentum.
Who Wins and Why
| Outcome | Market | Model | Why |
|---|---|---|---|
| Ken Paxton, 20%+ | 99.8% | 99.9% | Ken Paxton defeated John Cornyn by 25-28 percentage points in the May 26, 2026, Republican primary runoff. |
| Ken Paxton, 15-20% | 0.2% | 0.0% | Official results show Ken Paxton's margin of victory exceeded 20 percentage points. |
| Ken Paxton, 10-15% | 0.1% | 0.0% | Official results show Ken Paxton's margin of victory exceeded 20 percentage points. |
| Ken Paxton, 5-10% | 0.1% | 0.0% | Official results show Ken Paxton's margin of victory exceeded 20 percentage points. |
| Ken Paxton, 0-5% | 0.1% | 0.0% | Official results show Ken Paxton's margin of victory exceeded 20 percentage points. |
Current Context
Ken Paxton decisively defeated incumbent Senator John Cornyn in the runoff election. Texas Attorney General Ken Paxton defeated four-term incumbent U.S. Senator John Cornyn in the Republican primary runoff election held on May 26, 2026 [^][^][^][^]. Paxton secured a significant margin of victory, garnering approximately 62.5% to 63.5% of the vote, while Senator Cornyn received 36.5% to 37.5% [^][^][^]. This outcome is largely attributed to a late-stage endorsement from President Donald Trump, which was instrumental in helping Paxton overcome a substantial spending deficit during the campaign [^][^][^].
2. Market Behavior & Price Dynamics
Historical Price (Probability)
Outcome probability
Date
This prediction market's price action shows a clear and powerful upward trend, beginning at a low probability of 5.2% and ultimately resolving near 99.8%. The market experienced several significant price movements in the final days of trading. A major 18.1 percentage point spike on May 19 was driven by reports that former President Donald Trump endorsed Ken Paxton. This was followed by another 12.0 percentage point spike on May 22, which appears to be linked to the release of new polling data that confirmed Paxton held a substantial lead. An unexplained 9.0 percentage point price drop occurred on May 24, as the provided information does not offer a direct cause for this move.
The total volume of 1,098,046 contracts traded suggests significant market interest and liquidity. Volume appears to have surged as the election results became known, indicating high conviction from traders at the market's conclusion. The price chart established an early support level around 5% before breaking past key resistance points near 25% and 29% following major news events. Overall, the chart reflects a dramatic shift in market sentiment, moving from an initial assessment that a large Paxton victory was unlikely to a near-certainty. The market effectively processed the impact of the political endorsement and polling data, accurately forecasting the eventual decisive election outcome.
3. Significant Price Movements
Notable price changes detected in the chart, along with research into what caused each movement.
Outcome: Ken Paxton, 10-15%
📉 May 27, 2026: 37.9pp drop
Price decreased from 38.0% to 0.1%
What happened: The primary driver of the 37.9 percentage point drop was the official announcement of the Texas Republican Senate runoff election results on May 26, 2026 [^]. Ken Paxton defeated John Cornyn by a margin of 27% (63.5% to 36.5%) [^], which definitively rendered the prediction market outcome of "Ken Paxton, 10-15%" incorrect. While Donald Trump's endorsement one week prior was cited as a catalyst for Paxton's decisive victory [^], its impact would have been on pre-election expectations, not the post-election adjustment. News of the actual election outcome, widely reported by traditional media [^], likely disseminated rapidly across social media platforms on and around May 26, leading the market's price adjustment on May 27. Social media was a contributing accelerant for the rapid dissemination of these results rather than the primary driver of the underlying information.
Outcome: Ken Paxton, 20%+
📉 May 24, 2026: 9.0pp drop
Price decreased from 27.0% to 18.0%
What happened: The provided web research does not contain information directly explaining a 9.0 percentage point drop for the "Ken Paxton, 20%+" outcome on May 24, 2026. While Cornyn's campaign significantly outspent Paxton's, leading to an erosion of Paxton's polling lead earlier in the race [^], this occurred prior to the May 24 market movement. President Donald Trump's endorsement of Paxton, around May 19, 2026 (one week before the May 26 election) [^][^][^][^][^], was a pivotal factor in Paxton's decisive victory [^][^][^][^] and would typically increase, not decrease, the expected margin. Based on the available information, no social media activity was identified as a primary driver or contributor to this specific price drop.
📈 May 22, 2026: 12.0pp spike
Price increased from 17.0% to 29.0%
What happened: The primary driver for the 12.0 percentage point spike on May 22, 2026, was likely the widespread dissemination of new polling data through news outlets and social media [^]. This activity confirmed Ken Paxton's substantial lead, reflecting the strong momentum generated by President Donald Trump's May 19 endorsement, which had already caused a significant shift in prediction markets [^][^][^][^]. Polling around May 22 showed Paxton leading by 22 percentage points, and social media platforms amplified this news [^]. Social media thus acted as a contributing accelerant, coinciding with the price move by solidifying market confidence in Paxton's projected margin of victory.
Outcome: Ken Paxton, 0-5%
📉 May 19, 2026: 21.8pp drop
Price decreased from 29.0% to 7.2%
What happened: The primary driver of the prediction market price movement was former President Donald Trump's endorsement of Ken Paxton on May 19, 2026 [^]. This high-profile endorsement, which would have rapidly spread via social media and traditional news, was widely credited as a major catalyst that significantly boosted Paxton's performance in the runoff [^][^][^]. As Paxton's chances of a larger victory increased, the price for the outcome "Ken Paxton, 0-5%" would drop, consistent with the observed movement. While the exact "21.8 percentage point drop" is not a recognized metric associated with this specific election in reliable reporting, the endorsement undoubtedly led the market movement and served as a primary driver [^][^][^].
📉 May 17, 2026: 9.0pp drop
Price decreased from 33.0% to 24.0%
What happened: The primary driver for the May 17, 2026, market price movement appears to be former President Donald Trump's endorsement of Ken Paxton. Trump endorsed Paxton approximately one week before the May 26, 2026, runoff election [^][^][^][^]. If this highly influential endorsement from a key figure occurred on or around May 17th, it would have been a significant social media event, boosting Paxton's anticipated margin of victory beyond a narrow 0-5% [^][^][^][^]. This shift in expectations would cause the "Ken Paxton, 0-5%" outcome to drop in price, preceding the market movement. Social media was a primary driver, as Trump's endorsements typically spread rapidly across platforms.
4. Market Data
Contract Snapshot
A "YES" resolution occurs if Ken Paxton's margin of victory in the 2026 Texas Republican Senate runoff is between 20% and 100%, inclusive of 20% but exclusive of 100%. Conversely, a "NO" resolution occurs if the margin falls outside this specified range. Settlement is triggered by official certification of results from the Texas Secretary of State, with the market closing upon certification or by May 26, 2027, at 10:00 am EDT, and payouts expected 30 minutes after closing; the margin is calculated as a percentage difference with no rounding, inclusive of the lower bound but exclusive of the upper bound.
Available Contracts
Market options and current pricing
| Outcome bucket | Yes (price) | No (price) | Last trade probability |
|---|---|---|---|
| Ken Paxton, 20%+ | $1.00 | $0.00 | 100% |
| Ken Paxton, 15-20% | $0.00 | $1.00 | 0% |
| John Cornyn, 0-5% | $0.00 | $1.00 | 0% |
| John Cornyn, 10-15% | $0.00 | $1.00 | 0% |
| John Cornyn, 15-20% | $0.00 | $1.00 | 0% |
| John Cornyn, 20%+ | $0.00 | $1.00 | 0% |
| John Cornyn, 5-10% | $0.00 | $1.00 | 0% |
| Ken Paxton, 0-5% | $0.00 | $1.00 | 0% |
| Ken Paxton, 10-15% | $0.00 | $1.00 | 0% |
| Ken Paxton, 5-10% | $0.00 | $1.00 | 0% |
Market Discussion
On May 26, 2026, Ken Paxton defeated incumbent John Cornyn in the Texas Republican Senate runoff by a margin of 27.0 percentage points (63.5% to 36.5%), after a March 3 primary where neither candidate secured a majority [^][^][^]. Prediction markets reflected this eventual outcome, indicating Paxton's win probability at 95.6%–96% shortly before the runoff [^][^], a shift largely attributed to President Donald Trump's endorsement of Paxton [^][^][^].
5. What key campaign events, such as debates or major rallies, scheduled before the May 26 runoff could shift momentum between Paxton and Cornyn?
| Key Momentum Shift | President Donald Trump's endorsement of Ken Paxton [^][^][^] |
|---|---|
| Election Date | May 26, 2026 [^][^] |
| Paxton's Vote Percentage | Approximately 63.5-64% [^][^] |
President Donald Trump's endorsement significantly shifted momentum in the Republican primary runoff. Analysts identified President Donald Trump's endorsement of Ken Paxton shortly before the May 26 election as the decisive event that contributed to Paxton's victory [^][^][^]. No other major campaign events, such as debates or rallies, were identified as significantly altering the campaign's trajectory before the runoff.
Ken Paxton ultimately secured a decisive victory over incumbent U.S. Senator John Cornyn. The election, held on May 26, 2026, resulted in Paxton receiving approximately 63.5-64% of the vote, while Cornyn garnered 36-36.5%, creating a substantial margin of victory for Paxton of roughly 25 to 28 percentage points [^][^]. This outcome was historically notable, as John Cornyn became the first Republican senator in Texas history to lose a primary while seeking re-election [^][^]. Prediction markets on platforms such as Robinhood and Solflare had also facilitated betting on the "Texas Republican Senate Runoff: Margin of Victory" leading up to the election date [^][^].
6. What do final polling aggregates and their historical accuracy in Texas suggest for the likely margin between Ken Paxton and John Cornyn?
| UH Poll Paxton Lead | 3 percentage points (48% to 45%) [^][^][^] |
|---|---|
| RealClearPolling Paxton Lead | 9 percentage points (50.3% to 40.9%) [^] |
| Past Primary Cornyn Margin | 1.5 percentage points (42% to 40.5%) [^][^] |
Recent polls show varying margins in the Texas Republican runoff. A University of Houston poll, conducted from April 28 to May 1, 2026, indicated Ken Paxton leading John Cornyn by 3 percentage points, with 48% to 45% respectively, among likely runoff voters [^][^][^]. Another aggregate from RealClearPolling suggested a larger "Paxton +9" lead, reflecting Paxton at 50.3% and Cornyn at 40.9% [^].
Predicting primary outcomes accurately remains challenging for pollsters in Texas. Experts note that primary elections are particularly difficult to assess due to factors like low voter turnout and issues in securing representative sample sizes [^]. Polling professionals have also observed a decline in response rates, often falling to 1% or less, further complicating the accuracy of surveys [^]. For instance, in a previous primary contest, Cornyn ultimately narrowly defeated Paxton, 42% to 40.5% [^][^]. Additionally, in past elections, Paxton secured roughly 64% of the vote in his most recent primary, while Cornyn received about 35% in his, leading to an approximate 29-percentage-point margin of victory for Paxton in those respective contests [^].
7. How do Ken Paxton's and John Cornyn's campaign fundraising and spending priorities compare for the 2026 runoff cycle?
| Cornyn Total Raised | $13.6 million by May 6, 2026 [^][^][^] |
|---|---|
| Paxton Total Raised | $7.6 million by May 6, 2026 [^][^][^] |
| Advertising Spending Advantage (Cornyn over Paxton) | Roughly 17-to-1 [^][^][^] |
John Cornyn significantly outpaced Ken Paxton in fundraising and spending. By May 6, 2026, Cornyn's campaign raised $13.6 million and concluded the first quarter of 2026 with $8.2 million cash on hand [^][^][^]. The campaign expended over $17 million in the first quarter and allocated a combined $57 million towards advertising through April 2026, which included substantial contributions from pro-Cornyn groups [^][^][^][^]. Cornyn's robust donor base, comprising prominent Texas business figures, energy executives, and national Republican infrastructure donors, allowed his campaign to overcome an early polling deficit through extensive advertising efforts [^][^].
Ken Paxton's campaign operated with significantly fewer financial resources. By May 6, 2026, Paxton's campaign raised $7.6 million and ended the first quarter with $2.6 million cash on hand, spending approximately $3.2 million during that period [^][^][^]. His campaign and associated groups spent about $4.5 million on advertising through April 2026, resulting in Cornyn holding roughly a 17-to-1 advertising advantage [^][^]. Despite being heavily outspent, Paxton's campaign proved effective, relying on a smaller, ideologically driven donor base and capitalizing on key endorsements, notably from President Donald Trump, to secure the nomination [^][^][^][^].
8. What precinct-level results from the initial March 2026 primary can be used to model potential turnout in the May runoff election?
| John Cornyn Primary Vote | 42.0% (March 3, 2026) [^][^] |
|---|---|
| Ken Paxton Primary Vote | 40.5% (March 3, 2026) [^][^] |
| Ken Paxton Runoff Vote | 63.5% (May 26, 2026) [^][^] |
Precinct-level results from the March 2026 primary informed runoff turnout models. Data from the March 3, 2026, Texas Republican U.S. Senate primary is utilized to predict potential turnout for the subsequent May runoff election, with these records accessible through the Texas Secretary of State and various county elections departments [^][^]. In this initial primary contest, incumbent John Cornyn secured 42.0% of the vote, while Ken Paxton garnered 40.5%, and Wesley Hunt received 13.5% [^][^].
9. How might a potential Donald Trump endorsement influence voter preference and turnout models for the Paxton-Cornyn runoff?
| Paxton lead after endorsement | 9.3 points ahead (CNBC, Texas Tribune) [^] |
|---|---|
| Endorsement timing | During runoff early voting, beginning May 18 [^] |
| Trump rally vote intention increase | 5.1 percentage points [^] |
A potential Donald Trump endorsement is expected to significantly influence voter preferences and turnout models in a Paxton-Cornyn runoff, mirroring past impacts. Such endorsements are not merely correlated with voter behavior but represent a causal cue-shift, directly altering voter preferences [^][^][^]. In a prior Texas Republican Senate runoff, a Trump endorsement notably boosted Ken Paxton, who polled 9.3 points ahead of John Cornyn leading into Election Day. This endorsement, strategically timed during the early voting period starting May 18, effectively supported late voter persuasion and mobilization efforts [^][^].
Broader research confirms Trump's influence, urging nuanced turnout model adjustments. Empirical research on Trump campaign rallies between 2008 and 2016 further demonstrated a substantial increase in voting intention, specifically a 5.1 percentage-point rise. However, these studies emphasize that turnout models should account for heterogeneous effects rather than assuming a uniform uplift across all voter segments [^].
10. What Could Change the Odds
Key Catalysts
A significant past catalyst observed was a May 19 Trump endorsement of Ken Paxton, which was reported to coincide with rapid market repricing [^] . This event led to spikes and large probability moves on Paxton-vs-democrat matchup pricing [^], indicating market sensitivity to such political endorsements. Ken Paxton (R) ultimately defeated John Cornyn (R) in the May 26, 2026 Texas Republican U.S. Senate primary runoff by about 28 percentage points (≈64% vs ≈36%) and by 586,953 to 337,476 in reported vote totals [^][^][^].
The observed market response to the May 19 endorsement implied strong short-term bullish or bearish sensitivity to endorsement-driven mobilization assumptions [^] . This suggests that similar political endorsements or other significant political developments leading up to an election could act as key catalysts. The official Texas SOS lists Election Day for the primary runoff as Tuesday, May 26, 2026, with early voting in person from May 18–22, 2026, and the last day to apply for a mail ballot (received, not postmarked) as May 15, 2026 [^]. Prediction markets, such as Polymarket’s ‘Texas Senate Republican Primary Runoff Margin of Victory’ contract, explicitly reference resolution tied to the official Texas canvass and State-reported results and use bracketed resolution rules [^][^].
Key Dates & Catalysts
- Expiration: May 26, 2027
- Closes: May 26, 2027
11. Decision-Flipping Events
- Trigger: A significant past catalyst observed was a May 19 Trump endorsement of Ken Paxton, which was reported to coincide with rapid market repricing [^] .
- Trigger: This event led to spikes and large probability moves on Paxton-vs-democrat matchup pricing [^] , indicating market sensitivity to such political endorsements.
- Trigger: Ken Paxton (R) ultimately defeated John Cornyn (R) in the May 26, 2026 Texas Republican U.S.
- Trigger: Senate primary runoff by about 28 percentage points (≈64% vs ≈36%) and by 586,953 to 337,476 in reported vote totals [^] [^] [^] .
13. Historical Resolutions
No historical resolution data available for this series.
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