Representative Cory Mills of Florida is running for re-election in a solidly Republican district and has President Trump’s endorsement. Yet two of his fellow Republicans on Florida’s congressional delegation would prefer he lose his upcoming primary election.

Representatives Anna Paulina Luna and Mike Haridopolos took the rare step of endorsing one of Mr. Mills’s rivals this week, underscoring how vulnerable some Republicans consider Mr. Mills, who was investigated by the police in Washington, D.C., last year after a woman filed a report of assault. No charges resulted.

His former girlfriend was also granted a protective order against him. As a result of the various examinations, the House Ethics Committee is also investigating.

Mr. Mills has denied wrongdoing. But he has struggled to raise money, and Democrats have targeted his seat northeast of Orlando, which Mr. Trump won by 22 percentage points in 2024.

Ms. Luna and Mr. Haridopolos endorsed Ryan Elijah, a former local Fox television news anchor, who is one of three Republicans challenging Mr. Mills in the Aug. 18 primary.

“We need leaders in Congress who serve with integrity, energy, and an unwavering commitment to the people who sent them there,” they wrote in a joint statement on Wednesday.

Republicans have been fretting about potential losses by Mr. Mills and other embattled House members ahead of the November midterms.

Representative Chuck Edwards of North Carolina dropped his re-election bid this week after the House Ethics Committee recommended that he be censured for “persistent unprofessional and inappropriate conduct towards two young female staffers.”

Representative Max Miller of Ohio has been accused by his ex-wife, who is the daughter of one of the state’s Republican senators, of abuse against her and their young daughter. Mr. Miller has denied the allegations and vowed to remain in his re-election race.

Mr. Mills’s office did not respond to a request for comment on Thursday. “I’ve never been charged of an actual crime or misdemeanor,” he said in a debate on Wednesday night. “I’ve never actually had a mug shot of any sort.”

Ms. Luna, of St. Petersburg, Fla., is one of several Republican women who have had a hand in forcing the resignations of lawmakers accused of sexual misconduct.

“He is willing to put himself before his people, and he is willing to put himself before the party,” she said of Mr. Mills in an interview on Thursday. “I don’t want to serve with people like this.”

Mr. Haridopolos, whose district includes Cape Canaveral, on Florida’s Space Coast, said in an interview on Thursday that he had hoped Mr. Mills, like Mr. Edwards, would abandon his re-election bid. Republicans cannot risk solidly Republican seats in a midterm year expected to be difficult for the party, said Mr. Haridopolos, a former president of the Florida State Senate who also used to run political campaigns.

“If Congressman Mills is our nominee, we will lose the seat,” he said, adding that Democrats will spend heavily to remind voters about Mr. Mills’s “challenges.”

“If you Google his name, there’s just one story after another,” Mr. Haridopolos said. “I can do the math on this one.”

Hours after Ms. Luna and Mr. Haridopolos endorsed Mr. Elijah on Wednesday, Mr. Mills debated his three opponents for the first time. Mr. Elijah and another candidate, Michael Don Johnson, repeatedly raised Mr. Mills’s controversies; when asked if they disagreed with Mr. Trump on anything, Mr. Johnson went as far as to say that Mr. Trump made “a mistake” in endorsing Mr. Mills.

Mr. Mills remained feisty in his responses, casting himself as a fighter and mentioning Mr. Trump’s endorsement at least five times. “I’ve never cared about what the swamp wants or the swamp needs,” he said. He received plenty of applause in the debate, which was hosted by the Volusia County Republican Party.

Mr. Elijah said during the debate that the Seventh Congressional District is one that Republicans “should win.”

“We have to make the right choice Aug. 18,” he said, “to make sure the person that wins this race wins in November.”

Mr. Elijah’s campaign did not respond to a request for comment.

Irineo Cabreros contributed reporting.