Health Secretary Robert F Kennedy Jr defended his oversight of US health agencies in a fiery hearing on Thursday as lawmakers grilled him over his vaccine policies and other sweeping agency changes.
During three hours of testimony, Democrats accused Kennedy of lying and restricting Americans access to vaccines, while several Republican senators also raised concerns.
The hearing comes a week after Kennedy fired the leader of the US Centers for Disease Control and Prevention (CDC) in a clash over his vaccine policies.
Since taking the helm at the Department of Health and Human Services (HHS) in February, Kennedy has made a number of changes that have alarmed health experts.
In June, he fired every member of a panel of independent vaccine experts that issues recommendations for immunisations.
Public health experts raised concerns about the qualifications of the members - several of whom are vaccine critics - appointed in their place.
In a Wall Street Journal op-ed published on Thursday, Susan Monarez, the former head of the CDC, said she was fired because she refused to rubber-stamp vaccine recommendations from the panel.
During Thursdays hearing, the Senate Finance Committees ranking member, Democratic Senator Ron Wyden, pressed Kennedy on her accusations.
The health secretary denied her allegation, saying he told Ms Monarez to resign after asking her if she was a "trustworthy" person. He said she responded "no".
The vaccine advisory panel was one of several of Kennedys policy changes that lawmakers brought up during the hearing, leading to clashes.
As Senator Maggie Hassan accused the health secretary of restricting access to vaccines, Kennedy angrily responded: "Youre just making stuff up."
"Sometimes when you make an accusation, its kind of a confession, Mr Kennedy," Hassan said.
Lawmakers repeatedly questioned Kennedy over his stance on the Covid-19 vaccine, including Senator Mark Warner, who asked the health leader how many lives the shots had saved during the pandemic.
Kennedy said he did not know because of "data chaos" under the Biden administration.
"Youve had this job for eight months, and you dont know the data about whether vaccines saved lives?" Warner asked.
Kennedy later said the vaccine saved "quite a few" lives.
Republicans took a more measured tone with Kennedy, with some praising his leadership and others asking him to clarify what they described as contradictory remarks.
Senator Thom Tillis - who said before the hearing that he planned to ask Kennedy why his actions werent "matching up" with his promises - gave him a list of questions to answer at a later time.
The Republican lawmaker noted that Kennedy had accused some scientists of lying in his responses during the hearing.
"Id just like to see the scientific evidence of that," he said.
The toughest Republican questioning came from Senator Bill Cassidy, a doctor who gave a key vote to confirm Kennedy only after he gave him assurances that he would uphold several US vaccine policies.
Cassidy pressed Kennedy on his stance on Covid-19 immunisations, accusing him of restricting access to the shots because of conflicting recommendations from health agencies.
Under Kennedys leadership, the US Food and Drug Administration recently approved a round of Covid booster shots for fewer groups, only for adults 65 and older and people with medical conditions.
"Effectively, we are denying people vaccines," Cassidy said.
"Youre wrong," Kennedy responded.
Kennedys hearing comes a week after he fired 600 CDC employees in addition to Ms Monarez.
Just weeks before, a gunman fired 500 rounds at the CDCs headquarters in Atlanta, killing a police officer. Investigators say the shooter blamed the Covid-19 vaccine for making him suicidal.
Afterwards, hundreds of HHS officials wrote a letter to Kennedy, accusing him of fueling mistrust in public health officials by spreading misinformation.
They pointed to his statements about vaccines, including the Covid-19 shot and the immunisation against measles.
This year, the US has seen its worst outbreak of measles in decades.
While Kennedy has endorsed the vaccine as the best way to prevent the spread of measles, he has also made false claims about the safety and efficacy of the shot.