During a tense three-hour Senate committee session on Thursday, U.S. Health Secretary Robert F. Kennedy Jr. faced rigorous bipartisan scrutiny, attempting to justify his push to withdraw COVID-19 vaccine recommendations and the disruptions he has caused within federal health departments.

Kennedy criticized the credibility of the ousted CDC director, reiterated his previous anti-vaccine statements, and denied claims that individuals are experiencing difficulties obtaining COVID-19 vaccines.

Several medical associations, alongside numerous Democratic lawmakers, have urged for Kennedy’s dismissal. His interactions with Democratic senators often escalated into heated arguments, marked by shouting from both sides.

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

Republican senators highlighted that Kennedy praised former President Donald Trump, suggesting he merited a Nobel Prize for the rapid development of mRNA COVID-19 vaccines via the 2020 Operation Warp Speed, even though Kennedy has criticized the safety and ongoing utilization of those vaccines.

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

Tillis and others inquired about the CDC director’s recent dismissal, which occurred less than a month following her appointment.

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 who 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.

Democrats express hostility from the start

The Senate Finance Committee had called Kennedy to a hearing about his plans to “Make America Healthy Again,” but Democratic senators pressed Kennedy on his actions around vaccines.

At the start of the hearing, Sen. Ron Wyden of Oregon tried to have Kennedy formally sworn in as a witness, saying the HHS secretary has a history of lying to the committee. The committee’s chair, Sen. Mike Crapo of Idaho, denied the Democrat’s request, saying “the bottom line is we will let the secretary make his own case.”

Wyden went on to attack Kennedy, saying he had “stacked the deck” of a vaccines advisory committee by replacing scientists with “skeptics and conspiracy theorists.”

Last week, the Trump administration fired the CDC’s director 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.

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.

Shouting matches and hot comebacks

And the health secretary had animated comebacks as Democratic senators pressed him on the effects of his words and actions.

When Sen. Raphael Warnock, of Georgia, questioned Kennedy about his disparaging rhetoric about CDC employees before a deadly shooting at the agency this summer, Kennedy shot back: “Are you complicit in the assassination attempts on President Trump?”

Kennedy called Sen. Ben Ray Lujan of New Mexico “ridiculous,” said he was “talking gibberish” and accused him of “not understanding how the world works” when Lujan asked Kennedy to pledge to share protocols of any research Kennedy was commissioning into autism and vaccines.

He also engaged in a heated, loud exchanges with Sens. Elizabeth Warren of Massachusetts and Tina Smith of Minnesota.

“I didn’t even hear your question,” Kennedy replied to Sen. Catherine Cortez Masto as the Nevada Democrat repeatedly asked what the agency was doing to lower drug costs for seniors.

He also told Sen. Bernie Sanders that the Vermont independent was not “making any sense.”

Kennedy disputes COVID-19 data

In May, Kennedy – a longtime leader in the anti-vaccine movement – announced COVID-19 vaccines would no longer be recommended for healthy children and pregnant women, a move opposed by medical and public health groups.

In June, he abruptly fired a panel of experts that had been advising the government on vaccine policy. He replaced them with a handpicked group that included several vaccine skeptics, and then shut the door to several doctors groups that had long helped form the committee’s recommendations.

Kennedy has voiced distrust of research that showed the COVID-19 vaccines saved lives, and at Thursday’s hearing even cast doubt on statistics about how people died during the pandemic and on estimates about how many deaths were averted – statistics produced by the agencies he oversees.

He said federal health policy would be based on gold standard science, but confessed that he wouldn’t necessarily wait for studies to be completed before taking action against, for example, potential causes of chronic illness.

“We are not waiting for everything to come in. We are starting now,” he said.

A number of medical groups say Kennedy can’t be counted on to make decisions based on robust medical evidence. In a statement Wednesday, the Infectious Diseases Society of America and 20 other medical and public health organizations issued a joint statement calling on him to resign.

“Our country needs leadership that will promote open, honest dialogue, not disregard decades of lifesaving science, spread misinformation, reverse medical progress and decimate programs that keep us safe,” the statement said.

Many of the nation’s leading public health and medical societies, including the American Medical Association, American Public Health Association and the American Academy of Pediatrics have decried Kennedy’s policies and warn they will drive up rates of vaccine-preventable diseases.

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Stobbe reported from New York. Associated Press writer Mary Clare Jalonick contributed to this report.

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