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.

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.

The president is promising a return to meritocracy—while staffing his government with underqualified loyalists.

The Trump administration and new Republican majority in Congress have big plans to extend tax cuts and crack down on ...