Kennedy Jr. rejected characterizations of him as an anti-vaxxer in a Senate hearing Wednesday where senators will weigh his confirmation as Health and Human Services Secretary—as his former billionaire running mate threatens to fund primary challenges against lawmakers who vote against him.

Robert F. Kennedy Jr. has his first public appearance before the Senate today to discuss his nomination as secretary of the Department of Health and Human Services.

Robert F. Kennedy Jr.'s record of questioning childhood vaccine safety came under fire from a key Republican at the Trump HHS pick's confirmation hearing.

He needs to earn support from nearly all Senate Republicans to become Secretary of Health and Human Services (HHS).

Kennedy Jr. faced a plethora of tough questions on vaccines, abortion and public health policy during his Senate confirmation hearing Wednesday as President Donald Trump’s pick for secretary of Health and Human Services (HHS) Lawmakers pressed Kennedy,

The health committee chairman, Sen. Bill Cassidy, R-La., also has expressed concerns about Kennedy's anti-vaccine work. A physician, Cassidy said earlier this month he “had a frank conversation” and “spoke about vaccines at length” with Kennedy. On Tuesday, Cassidy told reporters that he is still unsure if he is backing Trump’s nominee.

Democrats focused on Kennedy's anti-vaccine advocacy. Republicans probed the former Democratic leader on his abortion and agriculture views.