Facing possible primary challenge from Trump ally, long-serving senator gets backing of leader Thune

As he gears up for what may potentially be his roughest re-election of his decades-long career, longtime GOP Sen. John Cornyn of Texas landed the backing of the top Republican in the Senate.

"I’ve been honored to work alongside @JohnCornyn—one of the most effective and respected conservative leaders in the country," Senate Majority Leader John Thune wrote in a social media post on Wednesday. 

Thune, who topped Cornyn last year in the Senate GOP race to succeed longtime leader Mitch McConnell, emphasized that his one-time rival "was tireless and instrumental in building our majority. We need to keep him in the Senate & in the fight to deliver on President Trump’s agenda."

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The Senate Majority Leader's endorsement came a couple of hours after Cornyn — who previously served six years as the No. 2 Republican in the Senate — officially launched his 2026 re-election campaign, as he bids for a fifth six-year term representing Texas on Capitol Hill.

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The backing from Thune, which was widely expected, comes as the 73-year-old Cornyn faces a possible primary challenge from Texas Attorney General Ken Paxton. The conservative and MAGA firebrand who's an ally of President Donald Trump has repeatedly for a couple of years flirted with taking on Cornyn.

"I can’t think of a single thing he’s accomplished for our state or even for the country," Paxton said in a September 2023 interview on the Fox News Channel. "Somebody needs to step up and run against this guy," adding, "everything’s on the table for me."

And in a Fox News Digital interview earlier this year, Paxton said that he's "looking potentially at the U.S. Senate."

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While Paxton is very popular with the conservative base of the party, political strategists note that toppling Cornyn in a GOP primary would likely be a very expensive proposition, and it's not clear if Paxton could raise the money needed for victory.

Paxton has claimed Cornyn does not represent the conservative values of Texans and accused him of not being an ally of Trump.

He has also regularly labeled Cornyn a "RINO," a "Republican in name only" and an insult MAGA and "America First" Republicans have regularly used to criticize more mainstream or establishment members of the GOP.

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Cornyn, during the early stages of the 2024 Republican presidential nomination race, had said he would prefer that the GOP take a new direction, which angered Trump. But the senator endorsed Trump in late January of last year, after the then-former president won both the Iowa caucuses and the New Hampshire primary, the first two contests in the Republican White House calendar.

Since Trump returned to the White House two months ago, Cornyn has been supportive of the president's cabinet nominees and agenda.

And in the senator's campaign launch video, the announcer highlights that during Trump's first term in office, "Texas Sen. John Cornyn had his back."

"Now I'm running for re-election and asking for your support so President Trump and I can pick up where we left off," Cornyn says to camera in the video.

Cornyn is a former state senator, former Texas Supreme Court justice, and former state attorney general, who first won election to the U.S. Senate in 2002.

Fox News' Peter Pinedo contributed to this report