Incumbent John Cornyn (R) and Ken Paxton (R) were the top two finishers among the eight candidates running in the Republican primary for U.S. Senate in Texas on March 3, 2026. Because no candidate received more than 50% of the vote, Cornyn and Paxton advanced to a runoff on May 26, 2026. As of March 2026, Cornyn, Paxton, and Wesley Hunt (R) led in polling, fundraising, endorsements, and media attention.

The Texas Tribune's Gabby Birenbaum described the primary as "expensive and brutal. Cornyn, a 23-year veteran of the Senate, has been in hot water with the Republican base over his efforts to pass a bipartisan gun safety bill in 2022 and past comments casting doubt on Trump’s political durability." Roll Call's Nathan L. Gonzales said the race was "an example of how data can be presented to paint whatever picture you want to see...Trump remains a wild card. His support is often the difference maker in Republican primaries, but he hasn’t made a decision in this race." Writing after Hunt joined the race in October 2025, the Associated Press' Thomas Beaumont said that "Hunt’s entry into the race raises the potential of a runoff for the GOP nomination."

Cornyn was first elected to the Senate in 2002. He earlier served as state attorney general and on the Texas Supreme Court. Cornyn said he had delivered for Texas while in office and was running for re-election "so President Trump and I can pick-up where we left off." The Texas Tribune's Owen Dahlkamp described Cornyn's strategy as "going all in on emphasizing his support for Trump — something he has been previously wary to do — to court the MAGA base that will be key to winning." Cornyn's campaign website said he had a "more than 99.2% voting record with President Trump — higher than Ted Cruz." Senate Majority Leader John Thune (R) and the National Border Patrol Council endorsed Cornyn.

Paxton had, as of the primary, served as Texas Attorney General since 2015. He was also a member of the Texas House for ten years and of the Texas Senate for two. The Texas Tribune's Jasper Scherer described Paxton's run as "the latest flashpoint in a power struggle between the Texas GOP’s hardline, socially conservative wing — which views Paxton as a standard-bearer — and the Cornyn-aligned, business-minded Republican old guard." Paxton's campaign website said that both "President Trump and Ken Paxton have been targeted in politically motivated witch hunts because there’s nothing that scares the establishment more than courageous conservatives who never back down from standing up for the American people." U.S. Reps. Lance Gooden (R) and Troy Nehls (R) endorsed Paxton.