Robert F. Kennedy Jr.’s tumultuous tenure as health secretary came to a head on Thursday as he faced tough questions during a hearing before the Senate Finance Committee.

During his nearly seven months in office, Mr. Kennedy has upended the Department of Health and Human Services, overseeing widespread changes to the institutes under his leadership. None has been hit harder than the Centers for Disease Control and Prevention, which recommends vaccines for Americans.

Mr. Kennedy, a longtime vaccine skeptic, has undermined immunizations; fired the C.D.C.’s independent advisers on vaccines and replaced them with vaccine critics; and ousted the center’s director less than a month into the job after she refused to fire top officials and rubber-stamp decisions from the advisers he had appointed.

Over three loud and contentious hours, Mr. Kennedy was remarkably combative and dismissive with senators, refusing to budge from his stance on vaccines, autism, Medicaid and the C.D.C.

Here are five takeaways from the hearing:

1. Both Republicans and Democrats pressed Mr. Kennedy on vaccine access.

“It’s been obvious from the start that Robert Kennedy’s primary interest is to take vaccines away from Americans,” said Senator Ron Wyden of Oregon, the committee’s ranking Democrat. “His actions reveal a steadfast commitment to elevating junk science and fringe conspiracies.”

He and other senators pushed Mr. Kennedy on the health secretary’s attempts to restrict access to vaccines. Under Mr. Kennedy’s leadership, health officials have narrowed who is eligible for updated Covid vaccines. Several senators, including Senator Bill Cassidy, Republican of Louisiana, pointed to the obstacles some Americans are facing in accessing the vaccines. Major pharmacies in some states are currently requiring that even people who are at high risk get prescriptions for the shots.