US President Donald Trump tightened his grip on the Republican Party on Tuesday as Kentucky voters ousted one of the few conservative lawmakers willing to challenge him openly. Congressman Thomas Massie's defeat, called by news networks including NBC and CNN about two hours after polls closed, marked another victory in Trump's campaign to punish Republican dissent. It follows the rout of Indiana state lawmakers who defied the US president on redistricting and the weekend collapse of Louisiana Senator Bill Cassidy's reelection bid. Massie's loss came after months of attacks from Trump, more than $32 million in ad spending and an unusual campaign appearance by Defense Secretary Pete Hegseth on behalf of Trump-backed challenger Ed Gallrein, turning a once-sleepy Kentucky primary into a national loyalty test. Several states held primaries Tuesday to pick candidates for the November midterm elections, but the standout contest was in Kentucky. Massie, a seven-term congressman, has been one of the president's most persistent internal critics. The race was being watched as a measure of whether Trump's grip on Republican voters remains strong despite war, inflation and sliding national approval ratings -- and whether there is still room in the party for lawmakers willing to break with him. Massie has angered Trump by opposing US military action in Iran and Venezuela, criticizing aid to Israel, resisting parts of the president's agenda and helping push for the release of files related to multimillionaire sex offender Jeffrey Epstein. Trump endorsed Gallrein, a farmer and retired Navy SEAL, in what US media have described as the most expensive House primary in American history -- much of the spending from pro-Israeli groups opposed to Massie. The president has spent months attacking the avowedly libertarian 55-year-old former engineer and inventor, labeling him a disloyal "moron," a "nut job" and a "major sleazebag." "Dealing with him is just horrible. I don't think he's a Republican...He's not a libertarian," Trump told reporters after polls opened. "Sometimes they say he's really a Dumb-ocrat. He votes against us all the time," added the president, who has recently taken to insulting Democrats with his alternative pronunciation.