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.

Republican Sen. Bill Cassidy, R-La., told Robert F. Kennedy Jr. on Thursday that he has been "struggling with your nomination" to lead the U.S. Department of Health and Human Services. Cassidy's comments came during the second hearing this week for Kennedy, President Donald… pic.twitter.com/zlLMfc2D0g

Robert F. Kennedy Jr. said he wasn’t antivaccine as senators pressed on his past remarks, in the first of two days of hearings over his nomination for health secretary.

The most powerful moment in two days of confirmation hearings for Robert F. Kennedy Jr., whom President Donald Trump nominated to head Health and Human Services, came from Louisiana Republican Sen. Bill Cassidy. A physician, Cassidy told Kennedy of an 18-year-old patient with hepatitis B who suffered from liver failure and needed a transplant.

Robert F. Kennedy Jr., a former presidential candidate and environmental activist, endorsed Donald Trump last year and threw his weight behind a campaign to “Make America Healthy Again.” For the past two decades he has been best known for airing skeptical views on vaccines.

As the U.S. Senate confirmation hearings continue for President Donald Trump’s Cabinet picks, PolitiFact is live fact-checking the hearings for FBI

During confirmation hearings, Robert F. Kennedy Jr., Kash Patel and Tulsi Gabbard faced tough senate scrutiny on their controversial pasts.

If approved, Kennedy will control a $1.7 trillion agency that oversees food and hospital inspections, hundreds of health clinics, vaccine recommendations and health insurance for roughly half the country.

Robert F. Kennedy Jr. has said vaccines are not safe. His support for abortion access has made conservatives uncomfortable.

PolitiFact is live fact-checking the confirmation hearings for Robert F. Kennedy Jr. and Kash Patel, two of President Donald Trump's Cabinet picks.

President Trump’s nominees for Health secretary, Commerce secretary, and Small Business Administration administrator are testifying before Senate committees, while Pam Bondi, Trump's choice for attorney general,