Washington DC - President Donald Trump's hold on his support base faces its latest test Tuesday, with voters deciding whether one of Congress's most independent conservatives can survive the Republican leader's full political firepower.
Several states are holding primaries to pick candidates for the November midterm elections, but the standout contest is in Kentucky, where Trump aims to oust seven-term Republican Thomas Massie, one of the president's most persistent internal critics.
The race is 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 has endorsed Ed Gallrein, a farmer and retired Navy SEAL, in what US media have described as the most expensive House primary in American history, with more than $32 million in ad spending – much of it from pro-Israeli groups opposed to Massie.
The president has spent months attacking the 55-year-old former engineer and inventor as disloyal, calling him a "moron," a "nut job," and a "major sleazebag."
"He is the Worst 'Republican' Congressman in History," Trump wrote on Truth Social, after telling voters at a March rally he wanted "somebody with a warm body" to beat Massie.
Thomas Massie looks to survive Trump's wrath with primary victory
Massie has cast the race as a test of independence inside the Republican Party.
"They want 100% compliance," Massie has said of the White House, arguing that he votes with Trump most of the time but is punished for the moments when he dissents.
The Kentucky showdown comes after Trump-backed forces routed Indiana state lawmakers who resisted his redistricting demands and after Louisiana Senator Bill Cassidy, who voted to convict Trump after the 2021 US Capitol riot, failed to make a runoff over the weekend.
A Massie defeat would send another warning to his party about the cost of crossing Trump, while a victory offers rare proof that Republican critics can survive the president's wrath.
Elsewhere on Tuesday, Georgia voters are choosing candidates in Senate and gubernatorial primaries, but the state's Supreme Court races may provide the clearest bellwether in a key swing state.
Democrats are trying to unseat two incumbent justices in contests that have drawn endorsements from Barack Obama and other party heavyweights. No incumbent Georgia Supreme Court justice has lost re-election in more than a century.