Donald Trump’s grip on Republicans tested in costly Kentucky primary

The US president’s power over his party will be tested in Kentucky on Tuesday night as renegade Republican Thomas Massie faces a Donald Trump-endorsed challenger in the most expensive House primary.

Fundraising groups have spent more than $33mn on ads in Kentucky’s fourth district, which stretches from the suburbs of Louisville towards Cincinnati and to the north-east hills of Kentucky, where Massie lives, according to AdImpact.

The libertarian-leaning representative, who has held the seat for 13 years, has emerged as one of Trump’s most prominent critics among Republicans in Congress, clashing with the president over the Iran war, the Epstein files and the landmark “Big Beautiful” fiscal legislation.

Trump has endorsed former Navy Seal Ed Gallrein, the rival candidate for the party’s nomination, in his latest move to oust those Republicans who dare criticise him.

Victory for Gallrein would demonstrate Trump’s hold over the party’s base. If Massie retains his seat, it will embolden Republican legislators to defy the president as they head into primaries to select candidates for November’s midterm elections.

“I think it’s a big risk for him,” Massie said of Trump in an interview with the FT last week. “He stands to gain not much, and he stands to lose a lot.”

Louisiana senator Bill Cassidy last weekend lost his Republican primary against a Trump-backed candidate, Julia Letlow.

The president on Tuesday endorsed Texas’s attorney-general Ken Paxton over John Cornyn, a senator for more than two decades. The president said Cornyn “was very late” to endorse him in the 2016 presidential campaign.

Trump has made clear his determination to seek revenge against Massie. In a Truth Social video supporting Gallrein this week, the president said: “He is fantastic, but forget that . . . Massie is the worst Congressman in the history of our country, always voting against Republicans and good values.”

Massie has opposed the president’s war against Iran, criticising the high cost and national security rationale for the conflict as well as the president’s decision to take action without congressional approval.

He also pushed for the release of files relating to late sex offender Jeffrey Epstein and voted against the multitrillion-dollar tax and spending legislation last year, known as the “One Big Beautiful Bill”, for massively raising US debt.

Billionaire pro-Trump donors such as Paul Singer, John Paulson and Miriam Adelson have given millions to Political Action Committees (Pacs) that oppose Massie. He is also opposed by the American Israel Public Affairs Committee, the pro-Israel campaign group, and the Republican Jewish Coalition.

“It’s a referendum on Israel’s influence,” Massie told the FT last week. “Can they buy a seat for a warm body in Kentucky?”

Defence secretary Pete Hegseth on Monday campaigned in Kentucky to paint the congress member as an obstructionist. “In the middle of a fight you don’t weaken your own side,” Hegseth said.

But Kentuckians say the issue is less a clash over foreign affairs and more a personality contest between Massie and Trump.

“The race feels close,” local Republican official Shane Noem told the FT. “The only conversation of substance we hear is: are you with the president, or are you with an independent voice, Thomas Massie?”