U.S. Health Secretary Robert F. Kennedy Jr., facing pointed bipartisan questioning at a rancorous three-hour Senate committee hearing on Thursday, tried to defend his efforts to pull back COVID-19 vaccine recommendations and explain the turmoil he has created at federal health agencies.

Kennedy said the fired CDC director was untrustworthy, stood by his past anti-vaccine rhetoric, and disputed reports of people saying they have had difficulty getting COVID-19 shots.

A longtime leader in the anti-vaccine movement, Kennedy has made sweeping changes to agencies tasked with public health policy and scientific research by laying off thousands of workers, firing science advisers and remaking vaccine guidelines. The moves — some of which contradict assurances he made during his confirmation hearings — have rattled medical groups and officials in several Democratic-led states, which have responded with their own vaccine advice.

Medical groups and several Democrats in Congress have called for Kennedy to be fired, and his exchanges with Democratic senators on the panel repeatedly devolved into shouting, from both sides.

But some Republican senators also expressed unease with his changes to COVID-19 policies.

The GOP senators noted that Kennedy said President Donald Trump deserved a Nobel Prize for the 2020 Operation Warp Speed initiative to quickly develop mRNA COVID-19 vaccines — and that he also had attacked the safety and continued use of those very shots.

“I can’t tell where you are on Operation Warp Speed,” said Republican North Carolina Sen. Thom Tillis.

Tillis and others asked him why the director of the Centers for Disease Control and Prevention was fired last week, less than a month into her tenure. Kennedy said she was dishonest, and that CDC leaders who left the agency last week in support of her deserved to be fired.

He also criticized CDC recommendations during the COVID-19 pandemic tied to lockdowns and masking policies, and claimed — wrongly — that they “failed to do anything about the disease itself.”

“The people at CDC who oversaw that process, who put masks on our children, who closed our schools, are the people who will be leaving,” Kennedy said. He later said they deserved to be fired for not doing enough to control chronic disease.

Trump was asked at a White House dinner with tech leaders on Thursday night if he has full confidence in what Kennedy is doing.

Trump said he didn’t watch the hearings but said of Kennedy, “he means very well.” Trump said Kennedy has “a different take, and we want to listen to all those takes.”

“It’s not your standard talk, I would say, and that has to do with medical and vaccines,” Trump said. “But if you look at what’s going on in the world with health and look at this country also with regard to health, I like the fact that he’s different.”

Last week, the Trump administration fired the CDC’s director — a Trump appointee who was confirmed by the Senate — less than a month into her tenure. Several top CDC leaders resigned in protest, leaving the agency in turmoil.

The ousted director, Susan Monarez, wrote in The Wall Street Journal on Thursday that Kennedy was trying to weaken public health protections.

“I was told to preapprove the recommendations of a vaccine advisory panel newly filled with people who have publicly expressed antivaccine rhetoric,” Monarez wrote. “It is imperative that the panel’s recommendations aren’t rubber-stamped but instead are rigorously and scientifically reviewed before being accepted or rejected.”

Kennedy told senators he didn’t make such an ultimatum, though he did concede that he had ordered Monarez to fire career CDC scientists. Monarez’s attorneys later responded that she stood by the op-ed and “would repeat it all under oath.”

Kennedy pushed back on concerns raised by multiple Republican senators, including Tillis and Sens. John Barrasso of Wyoming and Bill Cassidy of Louisiana. Both Barrasso and Cassidy are physicians.