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

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.

Robert F. Kennedy Jr., a former presidential candidate and environmental activist, endorsed Donald Trump last year and threw his weight behind a campaign to “Make America Healthy Again.” For the past two decades he has been best known for airing skeptical views on vaccines.

RFK Jr. claimed he is not “anti-vaccine” and appeared unfamiliar with key aspects of healthcare insurance programs in his confirmation hearing.

In a letter to senators, Caroline Kennedy etches a damning sketch of her cousin, the latest condemnation Robert F. Kennedy Jr. has received from members of his family.

Robert F. Kennedy Jr. was confronted with a number of his baseless claims and a vexing abortion issue. But Republican senators treaded lightly.

While Mr. Kennedy, seeking the job of health secretary, has been vocal about vaccines and his desire to overhaul the nation’s diet, he has said very little about other issues.

The hearings were packed to capacity with protesters and fans, while the spillover crowd hung out in hallways and overflow rooms.

The former U.S. ambasador — the last surviving child of Jacqueline and John F. Kennedy — urged lawmakers to reject RFK Jr.’s nomination as health secretary.