The chairman of the House Freedom Caucus, Congressman Bob Good, is facing a serious primary challenge after President Trump endorsed his opponent. Mr. Good, of Virginia, has been on the ropes since Speaker McCarthy got behind his opponent, John McGuire, a state senator.

The House Freedom Caucus consists of about 40 of America’s most conservative House members and has been involved in the downfall of two speakers of the House, John Boehner and Mr. McCarthy.

Now, the group’s leader, Mr. Good, is in the fight of his political life ahead of his June 18 primary election.

Mr. McCarthy’s opposition stems from Mr. Good’s vote — alongside seven other Republicans — to remove Mr. McCarthy from the speaker’s chair. After resigning from his seat in Congress, Mr. McCarthy has backed several primary challengers to members who voted to oust him, including Mr. Good.

Mr. McCarthy has backed challengers to Congresswoman Nancy Mace in South Carolina and Congressman Eli Crane in Arizona. In Tuesday’s primary election in South Carolina, Ms. Mace successfully fended off her primary challenger by more than 25 points.

In a statement after the election was called, Ms. Mace highlighted the challenger’s failure despite significant backing, saying “$7 million spent against us and we won it by 27 points. Most expensive primary in S.C. history.”

The challenge against Mr. Good, though, is fueled not only by the former speaker, but by that of a former president who is also the de facto presidential nominee of the Republican Party in 2024.

Trump’s issue with Mr. Good may come from the Republican presidential primary, when Mr. Good backed Governor DeSantis’s failed presidential campaign.

Although Mr. Good later endorsed Trump in January and made a pilgrimage to visit him in New York during his hush-money trial, it was too little, too late for Trump, who said that Mr. Good was “constantly attacking and fighting me until recently.”

“The damage had been done,” Trump said. “I just want to MAKE AMERICA GREAT AGAIN, and the person that can most help me do that is Navy SEAL and highly respected State Legislator, John McGuire, a true American Hero.”

Mr. McGuire has in turn characterized Mr. Good as an obstructionist who prevented Trump from executing an even more conservative policy platform as president.

“In 2016, Trump had the House and the Senate, but he had a few disloyal Republicans that kept rolling marbles under his feet, and trying to stop or slow down his agenda,” Mr. McGuire told a radio talk show host, John Fredericks.

Trump’s decision to deny Mr. Good his endorsement and instead endorse his challenger has even caused division among some of Trump’s most loyal devotees, like a former advisor, Steve Bannon, who is a fervent opponent of Mr. McCarthy.

A day after Bannon was ordered to report to prison by July 1 for defying a subpoena, he made the trip to Virginia to endorse Mr. Good at a rally, saying that Trump was wrong in his decision to endorse Mr. McGuire.

“We have unconditional support for President Trump,” Bannon said. “President Trump needs backup. We’re here today because these heroes fought McCarthy and the cartel and the establishment to a standstill.”

The combination of pressure from both Mr. McCarthy and Trump appears to be putting Mr. Good on the back foot. In a recent survey of the district by WPA Intelligence and the Virginia Faith and Freedom Coalition, Mr. McGuire led Mr. Good by 10 points.

Mr. Good did not immediately respond to a request for comment.