Who is Bill Cassidy, the Republican whose support is crucial for Kennedy?

In the end, Sen. Bill Cassidy, R-La., was a yes on Robert F. Kennedy Jr., at least for now.

Cassidy, a doctor, voted with the rest of the members of his party who sit on the Senate Finance Committee on Tuesday to forward Kennedy's nomination for health secretary to the full Senate, easing Kennedy's path to confirmation. Cassidy's approval ended a days-long drama in which he had publicly agonized over how to vote, given his deep unease with Kennedy's long history of questioning vaccines.

Shortly before casting his vote, Cassidy said in a statement that he had received "serious commitments" from the Trump administration in exchange for his support of Kennedy's nomination. Cassidy said that he had engaged in intense conversations with Kennedy and the White House -- including Vice President JD Vance -- since Kennedy's confirmation hearing last week.

"I've had very intense conversations with Bobby and the White House over the weekend and even this morning," the statement said. "I want to thank VP JD specifically for his honest counsel. With the serious commitments I've received from the administration and the opportunity to make progress on the issues we agree on like healthy foods and a pro-American agenda, I will vote yes."

The senator said he would explain his reasoning in a speech on the Senate floor later Tuesday morning. It is possible that he can vote no when the nomination reaches the Senate floor.

Louisiana is a deep-red state, one that Trump won by 22 percentage points in the 2024 election. Voting against Kennedy would have put Cassidy in peril for another reason: He is up for reelection in 2026 and facing a primary challenge from the right. But Cassidy's background as a specialist in liver disease -- and as a fierce advocate for vaccination -- gave him significant misgivings.

As chair of the Senate Committee on Health, Education, Labor and Pensions, the other panel before which Kennedy appeared for a confirmation hearing last week, Cassidy made several comments making clear that while he wanted to support Trump's pick, Kennedy's refusal to disavow some of his past claims about vaccines -- including that they cause autism, a theory that was long ago debunked -- was very much an issue.

"I'm a doc trying to understand," Cassidy said at one point. "Convince me that you will become the public health advocate, but not just churn old information so that there's never a conclusion."

Over the weekend, he posted on social media what many took as a hint: a quote from the Bible on the topic of courage.

"Joshua said to them: 'Do not be afraid; do not be discouraged. Be strong and courageous. This is what the LORD will do to all the enemies you are going to fight,'" Cassidy wrote on X, the social media site owned by Elon Musk.

Cassidy got his medical degree from Louisiana State University's School of Medicine, where he worked teaching medical students and residents at a hospital for the uninsured. During that time, in the early 1990s, he co-founded a community clinic that provided free dental and medical care to the working uninsured in his hometown of Baton Rouge, according to his official biography.

He also created a public-private partnership to vaccinate 36,000 residents in the Baton Rouge area against hepatitis B, at no cost to schools or patients. Cassidy opened Thursday's health committee hearing with a dramatic tale from his own medical practice: the story of a young woman, suffering from acute liver failure because of a hepatitis B infection, who had to be airlifted to a hospital for an emergency liver transplant.

"Now, the transplant, an invasive -- in 2000 -- quarter-of-a-million-dollar surgery that had a 5 to 10% mortality rate, but even if she survived, will leave her with a liver transplant and hospital bills every year of $50,000," he said.

"And as she took off," he continued, "it was the worst day of my medical career, because I thought, '$50 of vaccines could have prevented this all.' And that was an inflection point in my career, and since then, I have tried to do everything I can to make sure I never have to speak to another parent about their child dying due to a vaccine-preventable disease."

Throughout the Thursday hearing, Cassidy made clear that he worried Kennedy would use his star power and large following of "MAHA Moms" -- a reference to the movement Kennedy has dubbed "Make America Healthy Again" -- to continue to sow doubts about vaccination, which public health experts consider a singular triumph of their field. Vaccines have eradicated smallpox and nearly eliminated polio, diseases that were once major killers.

"My phone blows up with people who really follow you, and there are many who trust you more than they trust their own physician," Cassidy told Kennedy as the hearing began. "And so the question I need to have answered is, what will you do with that trust?"

In Louisiana, Cassidy's primary challenger, John Fleming, a former Congress member and current state treasurer, has cited the senator's vote to convict Trump on a single article of impeachment related to his role in the Jan. 6, 2021, attack on the U.S. Capitol.

Cassidy said in a statement at the time, "Our Constitution and our country is more important than any one person. I voted to convict President Trump because he is guilty."