Trump-backed challengers defeat Cassidy, testing his grip on Republicans

Bill Cassidy’s defeat in Louisiana on May 16 showed how punishing it can still be to cross Donald Trump inside the Republican Party. The veteran senator, who voted to convict Trump in the second impeachment trial after the Jan. 6, 2021, attack on the United States Capitol, finished third in the GOP primary and ended his bid for a third Senate term.

Trump-backed Rep. Julia Letlow and Louisiana Treasurer John Fleming advanced to a June 27 runoff, leaving Cassidy out of the race after more than two decades in public office. The result made Cassidy the first GOP senator to lose renomination in close to a decade, a sharp measure of how much Trump’s approval can still decide the boundaries of Republican politics.

Cassidy’s collapse came after months of pressure from the right, including Trump’s January 2026 endorsement of Letlow. Cassidy had drawn criticism from Trump allies over changes to the national vaccine schedule, and the primary became a direct test of whether Republican voters would punish a senator who had broken with Trump on impeachment. Instead, the race showed that a defiant vote in Washington could still carry a heavy price in Baton Rouge.

The Louisiana contest also carried broader warning signs for Republicans heading toward the midterms. A party built around Trump’s base may be able to discipline internal dissent more effectively, but that same discipline can leave Republicans with fewer candidates able to appeal beyond the president’s loyalists. In a general election year, that tension matters: contenders who survive a Trump-first primary can struggle to broaden their appeal to traditional conservatives and swing voters.

The political mood in Louisiana underscored that volatility. On the same night Cassidy fell short, voters rejected all five proposed constitutional amendments, a sweep that suggested a restless electorate and a state politics still in churn. For Republicans, the lesson was stark: Trump’s ability to settle primaries in his favor may strengthen his control over the party, but it can also narrow the coalition the GOP needs to win competitive races in November.