Sen. Bill Cassidy’s primary loss Saturday brings an end to a two-decade career in public office that was ultimately defined by tensions with President Donald Trump.

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And when Republicans have tensions with Trump, the president usually wins.

Cassidy failed to advance in the Republican primary in Louisiana, as Trump-backed Rep. Julia Letlow and state Treasurer John Fleming are projected to face off in a June 27 runoff. The winner in the GOP contest will be the heavy favorite this fall in ruby-red Louisiana.

The result marks another trophy for Trump’s collection in his ongoing bid to oust Republicans perceived as disloyal to him.

Throughout Cassidy’s career, there were occasional signs that the physician-turned-politician wasn’t quite in lockstep with his party on a handful of issues, including around health care. But Cassidy’s cardinal sin, in the eyes of Trump and his supporters, was voting in 2021 to convict the then-former president on impeachment charges of inciting an insurrection on Jan. 6.

Cassidy had just won re-election weeks earlier by a dominant margin. His vote after the impeachment trial was seen as something of a surprise by a senator not known for bucking his party once the dust settled.

It went against a pattern for Cassidy over his Senate tenure: a tendency to express moderate instincts and occasional disagreements with his party more through words than votes. This time, though, he broke with most of his party on the Senate floor.

“Our Constitution and our country is more important than any one person,” Cassidy said in a brief statement after the vote. “I voted to convict President Trump because he is guilty.”

And Trump never forgot it, having waged a largely successful campaign to oust Republicans who voted to impeach or convict him. Just two of the other six GOP senators who voted to convict Trump are still in office: Sen. Lisa Murkowski, R-Alaska, and Sen. Susan Collins, R-Maine. And just two of the 10 House Republicans who voted to impeach him are still in office, with only one running for re-election this year: Rep. David Valadao, R-Calif.

Cassidy’s vote to convict Trump came just a few months after the senator handily won re-election to his second six-year term. He was first elected to the Senate in the 2014 red wave, ousting Democratic Sen. Mary Landrieu. Before that, he served in the House for six years and the Louisiana state Senate for about two years.

It points to the tight grip that Trump maintains over a core GOP electorate that shares his unforgiving demands for lawmakers in the party be loyal to him.

It didn’t matter that Cassidy’s voting record has been closely aligned with Trump’s agenda in the Senate. The senator rarely ever voted against his legislative priorities, administrative personnel or judicial nominees in either term.

A recent ad by the National Republican Senatorial Committee highlighted Cassidy’s support for Trump’s “big beautiful bill” last year, saying, “Senator Bill Cassidy and President Trump kept their promise and delivered” on tax cuts.

Apart from Cassidy’s impeachment vote, his palpable discomfort with elements of Trump’s agenda and the “Make America Healthy Again” movement since the president won a second term in 2024 have gotten significant attention this year — even though, once again, his actual voting record didn’t stray.

In particular, there has been conflict between Cassidy, a doctor and outspoken proponent of vaccines, and Health and Human Service Secretary Robert F. Kennedy, a vaccine skeptic who has sought to infuse his philosophy into government policy. Cassidy, who chairs the Senate health committee that oversees Kennedy’s department, made his reservations clear last year.

But he still cast a pivotal vote to confirm him to the powerful position.

There again was that pattern for Cassidy, often sticking with his party in a final vote after expressing discomfort on the way there.

In 2017, when Republicans were gearing up to repeal the Affordable Care Act during Trump’s first year as president, Cassidy made a much-publicized appearance on ABC’s “Jimmy Kimmel Live” and said any health care bill must “pass the Jimmy Kimmel test” — named after his son, in that it won’t negative impact care for a child who was born with a congenital heart disease.

Cassidy went on to vote for the GOP effort, which rolled back protections for preexisting conditions. It narrowly failed in the Senate.

This year, in January, Cassidy said after Department of Homeland Security agents fatally shot two Americans in Minnesota, “The events in Minneapolis are incredibly disturbing. The credibility of ICE and DHS are at stake.” Still, he stood with his party on a series of votes amid Democratic demands to overhaul DHS enforcement practices.

His statement came just a week after Trump publicly called on Letlow to jump in the race, preemptively endorsing her and saying on Truth Social, “RUN, JULIA, RUN!!!”

Letlow launched her campaign three days later.

Now, she’s moving on to another round in the Republican primary. Cassidy is not.