Republican Sen. Bill Cassidy of Louisiana, a former physician who has spent his career touting the safety of vaccines, will likely determine whether Robert F. Kennedy Jr., a vaccine skeptic, becomes the country’s next Health and Human Services secretary.

He asked Kennedy to put aside his decades of voicing skepticism about vaccine safety and use his celebrity to encourage parents to vaccinate their children.

Kennedy, Jr., right, President Donald Trump's nominee to serve as Secretary of Health and Human Services, talks with Committee Chairman Sen. Bill Cassidy, R-La., following his testimony during a Senate Committee on Health,