Rep. Thomas Massie lost his primary Tuesday against Ed Gallrein, a huge win for President Trump's unprecedented campaign to oust the Kentucky Republican.Why it matters: Massie's loss sends another warning to Republicans about the dangers of crossing Trump, and shows that the president's broader political problems haven't diminished his power with the base.The race was Trump's last, and most important, stop on his revenge tour to oust Republican defectors.Trump's political operation launched an aggressive effort to unseat Massie last year, its first such effort to defeat a sitting Republican incumbent.The fight between Massie and Gallrein was the most expensive House primary in history, drawing more than $32 million in ad spending, according to AdImpact.Driving the news: Trump spent months portraying Massie as disloyal to the MAGA movement. He's called Massie a "moron," a "nut job" and a "major Sleazebag.""We're in a fight against the worst congressman in the history of our country," Trump said in an Oval Office video posted on Truth Social Monday.At a March rally in Massie's district, Trump said: "Give me somebody with a warm body to beat Massie, and I got somebody with a warm body, but a big, beautiful brain, and a great patriot."Gallrein is a farmer and former Navy SEAL officer hand-picked by Trump to challenge Massie.He's unequivocally backed the Trump agenda, saying Monday: "There has never been a more important time to stand behind our president."The other side: Massie contends the White House wants "100% compliance.""I vote with the President 90% of the time. I voted for the SAVE Act. I voted for DHS. In fact, by most scorecards, I'm the most conservative Republican, so it's only the 10% of the time they're mad about," he said.Catch up quick: Massie and Trump's contentious relationship dates back to Trump's first term.In 2020, Massie opposed Trump's COVID relief package, leading the president to call for Massie to be thrown "out of the Republican Party."Massie was also one of only two House Republicans to vote against Trump's "one big, beautiful bill" in 2025. Last summer, Massie sought to repair his relationship with the president, and House Speaker Mike Johnson (R-La.) was able to broker a truce, Axios previously reported.The ceasefire didn't last long. Days later, Massie ramped up his public criticism of the administration's handling of the Epstein files, and later led the push to release the files in defiance of Trump.Between the lines: Trump has taken out a number of Republican politicians who cross him.Sen. Bill Cassidy (R-La.), a top target of the president, lost his reelection bid on Saturday when he failed to finish in the top two in the state's GOP primary.Trump also exacted retribution on a group of Indiana Republican state legislators who blocked his push to redraw the state's congressional map.