Robert F. Kennedy, Jr. has expressed opposition to gender-affirming health care for transgender minors and questioned evidence linking HIV to AIDS, two issues that critics say should give senators second thoughts about confirming him as Health and Human Services secretary.

RFK Jr. would also have the power, along with the FDA commissioner, to slow down or hamper the process by which new vaccines are evaluated, approved, and recommended. That could discourage pharmaceutical companies from developing new or reformulated vaccines.