Robert F. Kennedy Jr.’s nomination to be the nation’s top health official is uncertain after a key Republican joined Democrats to raise persistent concerns over the nominee’s deep skepticism of routine childhood vaccinations that prevent deadly diseases.

Should Kennedy gain confirmation, he would oversee HHS’s $1.7 trillion budget and hold influence over the foods and drugs that affect the daily lives of Americans.

Kennedy Jr., President Donald Trump’s nominee to lead the Department of Health and Human Services, was back on Capitol Hill facing a second Senate panel in as many days as he vies for confirmation to lead a nearly $2 trillion agency.