On May 26, 2026, Texas Attorney General Ken Paxton beat three-term incumbent Sen. John Cornyn in the Texas Republican Senate primary runoff by a margin of nearly two to one. The win was Trump's; he had endorsed Paxton over Cornyn months earlier and campaigned actively for the challenger. Paxton, 63, now faces Democratic state Rep. James Talarico in November.
Cornyn, 74, was the senior Republican senator from Texas, a former Senate Majority Whip, and a member of the Senate Republican leadership. Trump's endorsement transformed him into a defeated incumbent. The Republican leadership-aligned Cornyn lost to a state attorney general who has been impeached by the Texas House (2023; acquitted by the Texas Senate), accused in multiple state and federal investigations, and accused of an extramarital affair that figured in the impeachment record.
The runoff was part of a broader Trump-administration sweep of the May 26 Texas primaries: Republicans are projected to gain 3-5 House seats in Texas, driven in part by mid-decade redistricting that produced an incumbent-on-incumbent Democratic runoff in which Rep. Christian Menefee defeated Rep. Al Green in TX-18.
The result is the clearest data point so far that Trump's threats against Senate Republicans who break with him (see Defense Secretary Pete Hegseth Headlined a Republican Primary Rally Against Rep. Thomas Massie, Breaking the Pentagon's Tradition of Political Neutrality, Tulsi Gabbard Resigns as Director of National Intelligence, the Fourth Trump Cabinet Member to Leave in 2026, Ending a Tenure Marked by the Politicization of Intelligence) are working: an incumbent senator with national leadership rank, defeated nearly two-to-one in his own party's primary, by a Trump-backed challenger.