Robert F. Kennedy Jr., President Donald Trump's pick to lead the top U.S. health agency, came under attack at a Senate confirmation hearing on Wednesday, with Democratic lawmakers accusing him of covering up his anti-vaccine views and embracing conspiracy theories to dissuade use of lifesaving medicines.

Kennedy sought to defend his record to the Senate Finance Committee, promising lawmakers that he was not against vaccines, and saying he would address rapidly increasing rates of chronic disease as well as follow Trump's direction on abortion.

"I believe that vaccines play a critical role in healthcare. All of my kids are vaccinated," said Kennedy, 70, who attended the hearing with his wife Cheryl Hines and some of his children. "We have the highest chronic disease burden of any country in the world... This is an existential threat."

If confirmed, Kennedy would run the U.S. Department of Health and Human Services, which oversees more than $3 trillion in healthcare spending, including agencies such as the Food and Drug Administration and the agency in charge of Medicare and Medicaid health insurance programs covering tens of millions of Americans.

The environmental lawyer is seen as a controversial pick on both sides of the aisle chiefly for having cast doubt on the safety and efficacy of vaccines.

During their questioning, Democratic senators brought up past statements from Kennedy made over decades, including that no vaccine was safe and effective. They quoted other Kennedy remarks made without evidence, including that COVID-19 was targeted to attack Caucasians and Black people, and that it was "highly likely" that Lyme disease was a military bioweapon.

"The receipts show that Mr. Kennedy has embraced conspiracy theories, quacks (and) charlatans, especially when it comes to the safety and efficacy of vaccines," said Democratic Senator Ron Wyden in an opening statement. "He has made it his life work to sow doubt and discourage parents from getting their kids lifesaving vaccines."

Democratic Senator Michael Bennet described Kennedy as someone who speaks with conviction but has a record that includes half truths and false statements.

"It doesn't matter what you come here and say," Bennet said. "It's not reflective of what you really believe."

Most of the nearly dozen Republican senators who questioned Kennedy on Wednesday appeared to support the nominee, with some expressing appreciation for his goals of tackling obesity, diabetes and other illnesses.

"Can't we come together as a nation and do this?" said Republican Senator Ron Johnson.

'50/50'

Finance Committee members will vote on whether to send Trump's pick to the full Senate for confirmation. A committee spokesperson said senators had until 5 p.m. (2200 GMT) on Wednesday to submit questions for the record, and Kennedy has to answer them all before a vote can take place.

Kennedy is also scheduled to appear in front of a Senate panel that oversees health on Thursday.