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.

Caroline Kennedy, daughter of former President John F. Kennedy, warned senators of her “predator” cousin ahead of his first confirmation hearing on Wednesday. In a letter first reported by The Washington Post, she wrote that his victims included family members and parents of sick children.

Kathleen "Kick" Kennedy is the eldest daughter of Robert F. Kennedy Jr., who could be confirmed as health secretary in Trump's administration.

Robert F. Kennedy Jr. will face the Senate for two days of confirmation hearings in a bid become the leader of Health and Human Services.

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.

Robert F. Kennedy Jr. faced intense scrutiny about previous statements at his first confirmation hearing for DHHS secretary.

Caroline Kennedy said in a scathing letter about her cousin, Robert F. Kennedy Jr., that she felt "an obligation to speak out."