Robert F. Kennedy, President Trump’s nominee for health secretary, vigorously defended his views on vaccines, and a key senator still has clear doubts.

Kennedy appeared on Wednesday and Thursday in front of the Senate’s finance and health committees, giving independent Sen. Bernie Sanders and Sen. Peter Welch, a Democrat, a chance to weigh in.

Robert F. Kennedy Jr. ‘s bid to be the nation’s top health official is uncertain after a key Republican joined Democrats to raise concerns over the nominee's skepticism of childhood vaccinations.