President Donald Trump endorsed Texas Attorney General Ken Paxton in the race for Republican Senate nominee ahead of next week’s runoff election, dealing a major blow to Senate leaders who backed Sen. John Cornyn throughout the primary.

Trump previously resisted weighing in on the nasty primary race, and publicly backed both candidates ahead of the March primary. Cornyn led by just one percentage point in that primary, earning 42% to Paxton’s 41%.

“I know Ken well, have seen him tested at the highest and most difficult levels, and he is a WINNER! Ken is a Strong Supporter of TERMINATING THE FILIBUSTER and, very importantly, THE SAVE AMERICA ACT,” Trump wrote in a post on Truth Social.

Early voting started on Monday for the May 26 runoff election, and many Republicans are anticipating a Paxton win, which may have pushed Trump to finally put his thumb on the scales. The president is also coming off of a successful effort to unseat an incumbent, after Sen. Bill Cassidy failed to advance to the runoff in Louisiana’s Republican primary on Saturday.

Trump made clear in his post that Cornyn fell short of the loyalty needed to receive his endorsement.

“John Cornyn is a good man, and I worked well with him, but he was not supportive of me when times were tough,” Trump wrote. “John was very late in backing me in what turned out to be a Historic Run for the Republican Nomination, and then, the Presidency, itself.”

Paxton has centered his campaign on his ability to better implement Trump’s agenda in Congress, hammering Cornyn over times the senator has disagreed with the president. A dedicated Trump ally, Paxton led the legal effort to overturn the 2020 election and has sued Democratic presidents, positioning Texas at the center of the conservative legal movement in battles over issues like abortion and religion.

But Paxton has also contended with a series of personal and political scandals. The Texas state House impeached him in 2023 for accusations of bribery, although he was acquitted by the state Senate and the federal government opted against corruption charges.

Republican leaders are worried that if he prevailed in May, Paxton’s baggage could jeopardize what has historically been a safe seat for Republicans.

Senate Majority Leader John Thune told reporters in March that he had fewer concerns about a Republican victory in November with Cornyn at the top of the ticket in a midterm year where Republicans are facing political headwinds. He has said he has repeatedly asked Trump to endorse the senator, who has served four terms in the Senate and carries high name recognition in Texas. Trump indicated to Thune during a phone call Monday that he planned to support the Texas attorney general.

Cornyn indicated to reporters on Monday that he did not expect to receive an endorsement from Trump ahead of the runoff election.

“I think that ship has finally sailed,” Cornyn told the Austin American-Statesman shortly after voting in Austin, Texas.

Cornyn said after the endorsement that Republican voters in Texas should still back him if they want to win in November.

“I have worked closely with President Trump through both of his Presidential terms and voted with him more than 99% of the time,” Cornyn posted on X. “He has consistently called me a friend in this race. It is now time for Texas Republican voters to decide if they want a strong nominee to help our GOP candidates down ballot and defeat Talarico in November, or a weak nominee who jeopardizes everything we care about.”

One Republican operative said they saw a poll recently showing Paxton up by double digits.

The Republican primary has been the most expensive in the nation, with committees and outside political groups spending more than $125 million to prop up Cornyn and Paxton’s campaigns. The National Republican Senatorial Committee and outside political groups spent more than $70 million on ads to defend Cornyn alone ahead of the March primary.

The winner will face Democratic nominee and state Rep. James Talarico for the seat in November. Talarico said in a statement that Trump’s endorsement has no bearing on his campaign.

“Our movement to take back Texas for working people rises above party politics — because the biggest fight in this country is not left versus right, it’s top versus bottom,” he said.

This article has been updated with a comment from Cornyn.