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.

The fate of Robert F. Kennedy Jr.’s bid to run HHS may rest with a Republican wrestling with his training as a physician and his instincts as a politician.

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,