President Donald Trump finally picked a side in the vicious Texas GOP Senate runoff, and the effect on prediction markets was immediate. Shortly after Trump’s announcement, Ken Paxton surged to 94% on both Polymarket and Kalshi. Meanwhile, incumbent Sen. John Cornyn was left trying to argue that incumbency still matters in a race that increasingly looks like a loyalty test rather than a normal Senate runoff. 

With the Texas GOP Senate runoff next week, Trump’s endorsement has taken what was already a brutal intra-party fight to another level as Senate Republicans are “livid” at the endorsement, according to multiple news outlets. That doesn’t appear to matter for prediction market traders.

They are reacting similarly to other 2026 midterm election primaries. Once Trump makes the race about him, the market usually stops treating the challenger as a challenger and starts treating the incumbent as an outgoing politician. Texas is now following that script.

Trump had mostly hung back in the Cornyn-Paxton fight long enough for the race to remain messy. Cornyn has worked to survive on seniority and establishment backing, while Paxton leans on his hard-right brand. 

But the endorsement settled the only question that really mattered in a runoff this close. Which candidate does Trump want his voters to rally behind? The answer was Paxton. And with that, markets immediately repriced the race as if the runoff had already been decided. Media outlets across the country all framed the endorsement as a decisive moment.

Paxton already had the advantage in the markets before Trump made his move, but the endorsement blew the doors off. What had been a Paxton lean is now a Paxton blowout in the books.

Cornyn’s case has always been simple. He is the sitting senator and the candidate with the easier path in a general election. But the runoff isn’t about the general election. Rather, it is about who wins the GOP’s internal test of identity, and Trump has made that test as plain as possible in recent elections like the Louisiana GOP Senate race Saturday and Kentucky GOP primaries Tuesday.

That is why Cornyn is in the dust now. The market is saying that incumbency can keep you alive in a lot of races, but it can’t save you when the party’s most influential figure publicly blesses the insurgent. The Texas Republican primary has become less about legislative record and more about whether Trump’s voters still want a senator who voted against the president.

The race is now extremely reminiscent of Louisiana’s GOP Senate primary. There, Trump’s candidate helped push an incumbent, Sen. Bill Cassidy, out, as two other candidates advanced to a runoff. Here, Trump has moved from backing chaos to officially endorsing it. The result here is similar, as a once-competitive race seems to have become a near-lock.

A 94% price is not just a prediction. That figure is a statement that the market believes the runoff has already become a turnout contest with the result heavily tilted toward the Trump-endorsed candidate. That is exactly what happened in other races this spring when the former president clarified his preference.

The market is not merely reacting to the endorsement as campaign news. It is pricing the Trump endorsement as the dominant variable in the race, which means the runoff is now less about whether Paxton can win and more about whether anything can stop him.

Cornyn’s remaining argument is that general election risk should matter more to Republican voters than raw loyalty. That’s what sitting GOP Senate leadership would prefer, according to reports. But that is a harder sell once Trump has entered the race directly.

Despite Trump’s approval rating still sitting at an all-time low, his influence in the 2026 GOP primaries is clear.  Once he endorses the challenger, prediction markets tend to stop treating the race as a toss-up and start treating it like a done deal.

The Texas GOP now looks even more likely to nominate a candidate who is deeply polarizing in the general election. Paxton could be a hard sell for independents wary of the president’s record this term.

That could keep the seat in play for Democrats and upstart State Rep. James Talarico. It also could increase trading volume in the Texas Senate general election market, which neared toss-up status on Kalshi and Polymarket on Tuesday. 

The post Trump’s Paxton Endorsement Has Prediction Markets Treating Texas Senate Runoff as a Done Deal appeared first on DeFi Rate.

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