President Donald Trump caught the Republican establishment off guard Tuesday when he endorsed Texas Attorney General Ken Paxton, his longtime ally and friend, instead of incumbent Sen. John Cornyn before voters finish casting their ballots next week in the Texas runoff for the Republican Senate nomination.

Cornyn, who’s in the toughest fight of his political life to keep his seat, had not been expecting Trump to issue an endorsement.

According to a source with knowledge of the matter, as late as Monday afternoon, Senate leaders believed Trump was going to stay out of the race, especially with the runoff just a week away.

However, in a phone call Monday evening between Trump and Senate Majority Leader John Thune, the president indicated he was planning on endorsing Paxton but stopped short of saying it outright, a senior Republican aide and a source familiar with the situation told NOTUS. Thune left the conversation with little clarity about what Trump would do, the aide added.

Thune said Tuesday that he found out about the endorsement via Trump’s Truth Social post.

“I found out the way I think everybody else did,” he said.

Senate Republicans were blunt about the fallout Trump’s decision could have on efforts to keep their majority in the upcoming midterms.

“This race could be the reason we lose the Senate,” one Republican familiar with state politics told NOTUS.

Sen. Lindsey Graham, a South Carolina Republican, acknowledged that the Texas Senate seat would be harder to hold if Paxton wins the runoff.

“I think Paxton can win, yeah, but I think it’d be three times more expensive,” Graham said Tuesday. “We’ve got to raise a lot more money now.”Alaska Sen. Lisa Murkowski told reporters that Trump’s endorsement “complicates” Republicans’ ability to hold onto their majority in November.

“The fact that the President would choose to endorse not Sen. Cornyn, but a candidate who probably is going to struggle mightily in the general, is a problem,” she said.

For months, Thune had tried to sway Trump toward endorsing Cornyn or, at the very least, staying out of the race, the aide said. But Trump had other plans.

The source with knowledge of the matter said Trump expressed that he was “pissed off” about Senate Republicans not eliminating the filibuster to pass his agenda and that senators were resisting his calls to fire the Senate parliamentarian over her decision that Republicans couldn’t include funding for his White House ballroom in a budget bill.

Following the recent primaries in Indiana and Louisiana, where the president successfully backed challengers to sitting GOP lawmakers who had displeased him, Trump felt emboldened and decided he wasn’t going to tolerate people who wouldn’t do what he wants, the source said.

Tuesday’s Paxton endorsement reflects this dynamic.

While the decision is sure to make the Republican base happy, those in the Senate are livid.

Some officials fear that Trump’s decisions to wade in against incumbents in Republican primaries has ruined his chances to legislate for the remainder of this Congress.

“Now he doesn’t have a governing majority,” the senior Republican aide said. “You pushed Tillis out, Lisa and Susan are independent, Cassidy has no fucking reason to do anything and now Cornyn has no reason to prostrate himself. Not to mention the other people who are just pissed off, ” the aide said, referring to North Carolina Sen. Thom Tillis, who is retiring, and the more moderate Murkowski and Maine Sen. Susan Collins.

“Good luck,” the aide continued. “If you think you’re going to govern between now and the midterms, that ain’t fucking happening. It’s very, very short-sighted.”

A Texas House member predicted something similar before Trump officially weighed in, saying the president “will have a Cornyn problem on his hands if he endorses Paxton.”

The way Paxton stayed alive and on Trump’s radar following a primary where he came in second to Cornyn is also under a microscope.

The day after the March primary, The Atlantic reported that Trump was expected to endorse Cornyn.

Some GOP operatives and Senate officials lay the blame for that never happening on the White House staffers who allowed the news of an expected endorsement to leak, which riled up the base in opposition to Cornyn, two sources told NOTUS.

“It’s just a bad look for them,” the senior Republican aide said of the White House.

The source familiar with the situation added that the White House’s inability to convince Republican Rep. Wesley Hunt to not run for the seat was a major blunder that led to Tuesday’s announcement.

“A botched job from the White House that is really going to hurt,” the source said. They added that if Paxton wins, not only could Republicans have to spend tens of millions of dollars to try to hold the Senate seat in November, but Paxton’s candidacy could also affect down-ballot races, especially two House seats in South Texas.

People also credit Paxton’s political strategy -– by saying he would only drop out if the Senate passes the SAVE America Act, a bill requiring proof of citizenship when registering to vote -– as a factor that shifted the conversation.

When reached for comment, the White House referred NOTUS to Trump’s social media post and Vice President JD Vance’s comments at a White House news conference.

“I think the message that people should take from this is fundamentally, you have got to serve the people who sent you, and if you don’t do that, you’re going to find yourself out of step with voters or out of step with the president United States, and that’s not a good place to be politically,” Vance said Tuesday.

Trump had planned to signal his displeasure with Senate leadership over its failure to bring the SAVE America Act, a top priority for him, to the floor by withholding his endorsement of Cornyn, one source close to the White House told NOTUS.

A separate source familiar with the talks between the White House and the Senate majority leader, given anonymity to speak freely, told NOTUS that conversations between Trump and Thune about an endorsement for Cornyn linked to a commitment to putting the SAVE America Act on the floor started March 4, a day after the Texas primary. The Senate eventually debated the legislation but four Republicans joined Democrats to block it in late April. Republican leaders signaled they did not plan to bring the bill up again.

The White House said “we don’t comment on private conversations” when NOTUS reached out about the discussions between Trump and Thune.

The response to the endorsement from Republicans on Capitol Hill was mixed.

Sen. Shelley Moore Capito, chair of the Senate Republican Policy Committee, expressed concerns that it could affect races across the country if Republicans have to divert resources to Texas.

“I think these are very competitive seats all around the country and resources are, as you heard John Thune say, one of the keys to success,” Moore Capito said Tuesday. “And any time you dilute it, and if it’s more competitive in a big state like Texas, that’s costly.”

The National Republican Senatorial Committee poured tens of millions of dollars into defending Cornyn, who has a long, storied past with Trump. The mudslinging got ugly and personal, with the Senate Republican campaign arm attacking Paxton using details of his divorce.

“What Ken Paxton has put his family through is truly repulsive and disgusting,” Joanna Rodriguez, a spokeswoman for the NRSC, said in a statement last July. “No one should have to endure what Angela Paxton has.”

Trump’s decision not to support Cornyn is not a huge surprise — the two haven’t always had the smoothest relationship. But since Cornyn eased off on his criticism of the president, he’s worked around the clock to show his allegiance to Trump.

After the president endorsed Paxton, Hunt, who failed to make the Senate GOP primary runoff, followed suit in a post on X.

“To EVERY supporter who believed in what we fought for, I am now asking you to unite behind the next United States Senator from Texas, @KenPaxtonTX. He has the total and complete endorsement of President Donald Trump, and he has mine as well. NOW is the time to come together, fight TOGETHER, and deliver a strong America First victory for Texas and for our nation,” he wrote.

Meanwhile, Republican lawmakers from Texas are already touting their allegiance to Paxton, and by extension, the president.

“Troy Nehls and I came out early for Ken because we saw early what President Trump confirmed today: Ken is the fighter we need in the Senate,” Rep. Lance Gooden, who backed Paxton the day the attorney general entered the race, told NOTUS.