Washington DC - A Louisiana senator bidding for a third term lost his Republican primary on Saturday – in the latest demonstration of President Donald Trump's hold over his party.

Trump had targeted Bill Cassidy and endorsed an opponent in retaliation for the senator voting to impeach him five years ago.

In the primary election Saturday, Cassidy was trailing in third place behind Trump-endorsed challenger Julia Letlow, a congresswoman, and state treasurer John Fleming, effectively shutting Cassidy out of a June 27 runoff vote, according to projections from CNN and NBC News.

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"Congratulations to Congresswoman Julia Letlow on a fantastic race, beating an Incumbent Senator by Record Setting Numbers," Trump posted Saturday night on his Truth Social platform.

The 79-year-old president was also quick to celebrate Cassidy's fall, writing in a follow-up post about the senator's projected election loss: "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's standing nationally has weakened amid economic frustration and divisions within the Republican coalition over the Iran conflict.

But among the deeply conservative voters who dominate Republican primaries, his influence remains formidable.

In addition to being one of seven Republican senators to vote in favor of impeaching Trump in 2021, Cassidy served as the key vote to confirm Trump's pick for health secretary, Robert F. Kennedy Jr.

A medical doctor by training who chairs the Senate committee focused on health, Cassidy has since criticized Kennedy's actions as health chief, including changing vaccine recommendations for children, saying doing so would "make America sicker."