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.

BATON ROUGE, La. (AP) — Sen. Bill Cassidy has emerged as a central figure in the confirmation of Robert F. Kennedy Jr., whose nomination to health and human services secretary poses an equally consequential moment for the second-term Republican facing an uncertain political future in Louisiana.