Robert F. Kennedy Jr. is on shaky political ground after two days of contentious confirmation hearings on Capitol Hill failed to lock in enough Senate votes for him to become health and human services secretary.

Sen. Bill Cassidy, the top Republican on the Senate Committee on Health, Education, Labor and Pensions, concluded Thursday's hearing by saying he was "struggling" with the nomination due to Kennedy's vaccine positions. Kennedy notably refused to say vaccines don't cause autism as he faced pointed question from lawmakers.