John Cornyn

President Donald Trump's endorsement of Texas Attorney General Ken Paxton over incumbent Sen. John Cornyn, R-Texas, upended the state's high-stakes Senate race Tuesday, tightening the contest and briefly giving Democrats an edge in prediction markets tracking the race.

The endorsement immediately rattled Republican odds in the closely watched 2026 contest, with prediction platforms Kalshi and Polymarket both showing sharp movement toward Democrat nominee James Talarico, a Texas state representative who has emerged as a top Democratic Party fundraiser and one of the party's most closely watched candidates.

Kalshi briefly showed Talarico as the favorite to win the November general election before Republicans recovered a narrow lead later Tuesday.

By midafternoon, Kalshi gave Talarico a 49% chance of victory, up from about 44% at the beginning of May.

Republican odds fell as low as 48% after Trump announced his backing of Paxton before rebounding slightly to 51%, still well below the 57.2% chance Republicans held earlier this month.

Polymarket showed a similar trend.

Republican odds dropped from 55% Monday to 51% Tuesday afternoon, while Talarico's chances surged from 42% Tuesday morning to briefly leading at 51% before settling back to 49%.

Trump announced the endorsement in a Truth Social post Tuesday, praising Paxton as a loyal ally and supporter of his political agenda.

"The Highly Respected Attorney General of Texas, Ken Paxton, an America First Patriot, and someone who has always been extremely loyal to me and our AMAZING MAGA MOVEMENT, is running for the United States Senate, to represent a place I love and WON, BIG, three times, with 6.4 Million Votes in 2024 (The Most Votes in the History of the State, BY FAR)!" Trump wrote.

Trump also described Paxton as a "'true MAGA Warrior'" and highlighted his support for ending the Senate filibuster and bolstering Trump-backed election legislation.

The endorsement marked a major blow to Cornyn, who had spent months seeking Trump's support in the increasingly bitter Republican runoff campaign.

Cornyn, a four-term senator first elected in 2002, has argued he would be a stronger general election candidate against Democrats in a state Republicans have controlled for decades but where Democrats believe demographic shifts and voter frustration could create an opening.

Paxton has long been one of Trump's closest allies in Texas politics and became nationally known for backing Trump's challenges to the 2020 presidential election results.

He also survived a 2023 impeachment trial in the Texas Senate after being accused of corruption and abuse of office by the Republican-led Texas House.

Vice President JD Vance on Tuesday criticized Cornyn's inability to secure Trump's endorsement.

"I've known John Cornyn a long time," Vance told reporters at the White House. "But unfortunately, when it really counted, Ken Paxton was there for the country and for the president, and that's why he ultimately earned the president's endorsement."

The Texas Senate race is expected to become one of the most expensive and competitive contests of the 2026 election cycle.

Democrats have not won a Senate race in Texas since 1988.