Trump-backed Ed Gallrein defeated Rep. Thomas Massie in Kentucky's 4th Congressional District Republican primary on Tuesday, CBS News has projected. 

Massie is the latest incumbent Republican to fall in a primary to a challenger endorsed by President Trump, who has successfully targeted a number of Republicans he has deemed his adversaries in recent primaries. 

Last week, Massie referred to himself as the "main event" on Mr. Trump's revenge tour. 

The race in northern Kentucky was the most expensive House primary in history, with pro-Israel interest groups pumping millions in the contest in a bid to unseat Massie, who has been a thorn in Mr. Trump's side. 

In an interview with CBS News on Monday, Massie said spending by pro-Israel interest groups caused more disruption in the race than the president. In a typical year, Massie said he would have won the primary with 80% of the vote. He estimated Mr. Trump's endorsement of Gallrein lowered his support to 60%, and spending from the pro-Israel lobby further eroded it. 

"I think what would have been a 60-40 race is now a 50-50 race," Massie said, citing Gallrein's support from AIPAC, the Republican Jewish Coalition and GOP megadonors such as Miriam Adelson. 

Massie voted against Mr. Trump's signature tax-cutting legislation, known as the One Big Beautiful Bill Act, last year and spearheaded the effort to force the Justice Department to release materials related to convicted sex offender Jeffrey Epstein. He has also opposed the war with Iran and has questioned the legality of the military operation to capture former Venezuelan President Nicolás Maduro and the strikes on alleged drug smuggling boats around Venezuela. 

His opposition provoked Mr. Trump, who campaigned for Gallrein, a former Navy SEAL. 

"They want 100% compliance," Massie said. 

In recent days, Mr. Trump lashed out at Massie and congressional Republicans who campaigned on his behalf. The president called Massie the "worst 'Republican' congressman in history" and said he would support a challenger to one of those Republicans, Rep. Lauren Boebert of Colorado, whom he called "weak minded." 

Defense Secretary Pete Hegseth traveled to Kentucky on Monday to campaign with Gallrein, arguing that the candidate would fall in line behind Mr. Trump. Hegseth said he was there in his personal capacity, though the visit marked a break from the longstanding practice of military officials avoiding partisan activities. 

"When the movement needs unity, especially at the biggest moments, Massie is willing to vote with Democrats," Hegseth said. "President Trump needs reinforcements, and that's what war fighters do. They stand behind leaders and have their back. War fighters understand mission, they understand teamwork, they understand loyalty. And they understand that in the middle of a fight, you don't weaken your own side." 

House Speaker Mike Johnson, a Louisiana Republican, declined to endorse Massie, telling reporters last week that he was staying out of the race. 

"It's no secret that Thomas Massie has been critical of me at times, but I don't ever take any of that personally," Johnson said. 

Still, Johnson acknowledged that it would be "helpful to have a more reliable vote" as Republicans manage a narrow majority in the lower chamber. 

Massie said last week that his loss would disenfranchise a swath of Republican voters who helped the party win the White House and the House majority. 

"If I'm gone … the tent has significantly been diminished and will make winning the majority harder in the fall," he said. 

Massie has represented the district since 2012, when he won a special election to replace GOP Rep. Geoff Davis who resigned citing a "family health issue."