US President Donald Trump and Health Secretary Robert F. Kennedy Jnr succeeded in their efforts to defeat Senator Bill Cassidy in Louisiana’s Republican primary, a signal of the enduring strength of the president’s hold on his party despite an unpopular war and soaring fuel prices.

Cassidy was one of seven Republican senators in 2021 who voted to convict Trump on the charge of inciting an insurrection on January 6 that year. He placed last in a three-way race on Saturday against Representative Julia Letlow, who was endorsed by both Trump and a Kennedy-linked political action committee, and State Treasurer John Fleming.

“His disloyalty to the man who got him elected is now a part of legend, and it’s nice to see that his political career is OVER!” Trump said of Cassidy on social media late on Saturday.

With 92.3 per cent of ballots tallied, Letlow has 44.8 per cent of the vote and Fleming has 28.3 per cent. Cassidy trailed with 24.7 per cent of the vote.

Letlow and Fleming will advance to a run-off next month. Whoever wins that contest is virtually assured victory in November in the deep red state. In his re-election race in 2020, just months before his vote to convict Trump, Cassidy won 59 per cent of the vote.

In a primary season where Trump is crusading to vanquish members of his party with whom he has been at odds, the Louisiana race comes just days before the president tries to oust another Republican foe, Representative Thomas Massie, in Kentucky.

But Trump has also opted so far to stay out of a hard-fought Texas run-off later this month between incumbent Senator John Cornyn, a traditional conservative, and state Attorney General Ken Paxton, who is more politically aligned with the president.