Republican Sen. Thom Tillis lambasted Democrats for their questioning and criticism of Kennedy's views.

Tills asked Kennedy bluntly if he were a conspiracy theorist.

"That is a pejorative that's applied to me, mainly to keep me from asking difficult questions," Kennedy said before saying he was proven right by recent studies but also making unproven claims about the COVID vaccine and fluoride.

Kennedy’s endorsements of the measles and polio vaccines during today’s confirmation hearing mask his years of skepticism about their safety and effectiveness.

Here are some medical claims made by RFK Jr. that are missing context or include falsehoods.

Kennedy claimed the CDC approved the COVID-19 vaccines without scientific basis, however, vaccines are among the most studied vaccines in history, with large clinical studies showing the health benefits far exceed any potential risks.

Kennedy claimed he had nothing to do with the measles outbreak in American Samoa. Eighty-three people died during that outbreak. The nation's Ministry of Health cited Kennedy's visit and rhetoric as exacerbating vaccine hesitancy at a crucial moment.

The nominee claimed he 'probably" said Lyme disease is "highly likely a military-engineered bioweapon," however the disease is caused by a type of bacteria and spreads through the bite of blacklegged ticks.

Kennedy said he has never claimed pesticides lead children to become transgender, however, he has repeatedly pushed unfounded claims that environmental toxins, including those in drinking water, are linked to gender identity in children.

-ABC News' Will McDuffie, Youri Benadjaoud and Sony Salzman

Under the Biden administration's Inflation Reduction Act, Medicare for the first time was allowed to directly broker with drug manufacturers. The first 10 drugs subject to negotiations were announced in 2023 and 15 additional drugs were unveiled just before President Joe Biden left office.

Democratic Sen. Catherine Cortez Masto looked for a commitment from Kennedy to protect those negotiations going forward, as Trump and many Republicans campaigned last year on rolling back the law.

"Are you there to be a rubber stamp to this administration?” she asked him.

Kennedy claimed the White House issued a new executive order supporting the drug pricing negotiations under the law, though no such executive order has been released.

"[Trump] has instructed me, and I've met with him repeatedly, as that we need lower price seniors in this country," Kennedy said.

Sen. Steve Daines, R-Mont., asked Kennedy if he would take action to review the regulatory actions behind the abortion drug mifepristone.

Mifepristone is an oral drug typically used in combination with another drug, misoprostol, to induce an abortion or to help manage an early miscarriage.

The medication works by blocking progesterone, a hormone that the body needs to continue a pregnancy. The Food and Drug Administration said it is safe to use as indicated and directed.

Daines expressed concern that mifepristone labeling lists emergency room visits as a possible complication. ER visits are not always considered a serious adverse event by health care professionals.

Kennedy said Trump has asked him to study the safety of mifepristone and that the president has not taken a stance on how to regulate the medication.

"Whatever he does, I will implement those policies and I will work with this committee to make those policies make sense," he said.

Republican Sens. Bill Cassidy and Rand Paul, both doctors, had a brief argument over the Hepatitis B vaccine for infants.

Cassidy defended the vaccine's efficacy amid Paul's questioning of some of its uses: "A vaccine on day one of life prevents chronic Hepatitis B 95% of the time."