NEW ORLEANS (AP) — U.S. Sen. Bill Cassidy is fighting for his political life in Louisiana's Republican primary on Saturday as he faces a challenge backed by President Donald Trump, the latest attempt by the president to purge the party of politicians he views as disloyal.

Trump endorsed U.S. Rep. Julia Letlow over Cassidy, in an unusual attempt to dislodge an incumbent senator. Cassidy voted to convict Trump in his second impeachment trial, stemming from the attack on the U.S. Capitol on Jan. 6, 2021. Cassidy, a doctor, has also clashed with Health Secretary Robert F. Kennedy Jr. over vaccine policy, even though he provided crucial support to help Kennedy get confirmed.

The president unloaded on Cassidy on Saturday morning, calling him "a disloyal disaster" and "a terrible guy" on social media. Trump criticized the senator's impeachment vote and said "he's going to get CLOBBERED," adding that Letlow is "a winner who will NEVER let you down."

A third candidate is state Treasurer John Fleming. If no one gets at least 50% of the vote, a runoff will be held June 27.

The winner will almost certainly take the November general election because of the state's Republican leanings.

The election was scrambled by a recent U.S. Supreme Court decision gutting a part of the Voting Rights Act that affects how congressional maps are drawn. Although the Senate primary is moving forward, Louisiana leaders decided to delay House primaries until a future date to allow them to redo district lines ahead of time, a shift that could cause confusion for voters on Saturday.

A senator tries to hang on

Cassidy has waged an aggressive campaign to convince voters he should not be counted out.

"Four months ago I would have told you it's impossible for Cassidy to win this," said Mary-Patricia Wray, who has consulted for Republican and Democratic candidates in Louisiana. "I still think it's statistically unlikely, but no longer impossible."

Paul Begue, a 41-year-old in New Orleans who works in the agriculture industry, said he planned to vote for Cassidy. He was bothered by a video of Trump saying Letlow was "as loyal as can be." For Begue, that was "the final nail in the coffin."

"I don't care about her loyalty to President Trump," he said, adding, "I like elected officials that seem to make their own decisions."

The senator's campaign is expected to have spent roughly $9.6 million on advertising through May 16, according to the ad-tracking firm AdImpact. And Louisiana Freedom Fund, a super PAC supporting him, is on track to spend $12.3 million.

By comparison Letlow's campaign, which launched Jan. 20, has spent roughly $3.9 million, while a super PAC backing her, the Accountability Project, has spent about $6 million since then.

Fleming's campaign has spent about $1.5 million.

Cassidy and Louisiana Freedom Fund ran ads attacking Letlow within days of her entering the race for supporting diversity, equity and inclusion initiatives, which Trump has tried to root out of the federal government.

Letlow, a college administrator before her election to the House, said she supported DEI while interviewing for the position of president of University of Louisiana-Monroe in 2020.

The ads, an attempt to characterize Letlow as a progressive trying to pass as a conservative, are one way Cassidy is trying to flip the script in a race where he's on the outs with Trump.

The president targets Cassidy

The senator's vote in favor of convicting Trump after his 2021 impeachment over the Jan. 6 Capitol siege has shadowed Cassidy throughout his second Senate term.

John Martin, a 68-year-old retired engineer in south Louisiana, said he would vote for Letlow because he was still upset by Cassidy's decision. He waved a flyer from Letlow's campaign showing her standing alongside the president.

"I know a lot more about Cassidy than I do about her," Martin said. "But if she's endorsed by Trump, I'm going to believe that."

Cassidy steered clear of Trump's ire last year, supporting Kennedy to lead the Department of Health and Human Services despite his public reservations about the nominee's anti-vaccine views.

Mark Workman, a 75-year-old retired infectious disease physician in the New Orleans suburbs, said he backs Fleming. Had Cassidy "stood up and blocked RFK," Workman said, he would have supported the senator for taking a strong and courageous stance.

"He had the ability to stop him," Workman said, "and he was too weak to do that."

As chair of the Senate health committee, Cassidy has been more publicly critical of Kennedy, including over funding cuts for vaccine development.

Trump blamed Cassidy for the failed nomination of his second choice for surgeon general, Casey Means, who raised doubts about vaccinating newborns for hepatitis B, a practice Cassidy supports.

Trump withdrew the Means nomination and blasted Cassidy.

"Hopefully all of the Great Republican People of Louisiana, which I won, BIG, three times, will be voting Bill Cassidy OUT OF OFFICE in the upcoming Republican Primary!" Trump posted on social media.

Republican Gov. Jeff Landry's decision to postpone the congressional primaries may weigh against Cassidy. It could dampen turnout among voters who are less fervently pro-Trump, Wray said, especially if there is confusion about the schedule.

"Suspending the congressional primaries hurts Cassidy," she said. "Some people believe the Senate primary is canceled."

Cassidy complained Friday that the new primary system enacted last year was confusing voters by requiring them to ask for a partisan ballot instead of the previous all-party primary that had been in place. He said some called his office to say they had been unable to vote for him.

"The process that was set up was destined to be confusing," Cassidy told reporters.

A challenger waited for Trump's backing

Letlow considered running last year but only entered the race after Trump announced his endorsement in January.

By that time Fleming, a former House member and Trump administration official who was elected state treasurer in 2023, was already in the race as a Trump devotee. But Landry was looking for a better-known challenger, and he suggested Letlow to the president.

Letlow had an unconventional and tragic entry into politics.

In 2020, while she was a college administrator, her husband Luke was elected to the U.S. House but died of COVID-19 before he could be sworn in. Letlow ran for and won the seat in a March 2021 special election and was reelected in 2022 and 2024.

Beaumont reported from Des Moines, Iowa.