U.S. Health Secretary Robert F. Kennedy Jr., facing pointed bipartisan questioning at a rancorous three-hour Senate committee hearing on Thursday, tried to defend his efforts to pull back COVID-19 vaccine recommendations and explain the turmoil he has created at federal health agencies.

Kennedy said the fired CDC director was untrustworthy, stood by his past anti-vaccine rhetoric, and disputed reports of people saying they have had difficulty getting COVID-19 shots.

Medical groups and several Democrats in Congress have called for Kennedy to be fired, and his exchanges with Democratic senators on the panel repeatedly devolved into shouting, from both sides.

But some Republican senators also expressed unease with his changes to COVID-19 policies.

Kennedy told Sen. Bernie Sanders that the Vermont independent was not “making any sense” during his line of questioning and engaged in heated, near shouting exchanges with Sens. Elizabeth Warren of Massachusetts and Tina Smith of Minnesota.

Kennedy called Sen. Ben Ray Lujan of New Mexico “ridiculous,” said he was “talking gibberish” and accused him of “not understanding how the world works" as Lujan asked about Kennedy’s past comments on autism and vaccines.

When Sen. Raphael Warnock, D-Ga., questioned Kennedy about his disparaging rhetoric about CDC employees before a deadly shooting at the agency this summer, Kennedy fired back at the Georgia Democrat: "Are you complicit in the assassination attempts on President Trump?"

Kennedy also pushed back on concerns raised by multiple Republican senators, including Sens. John Barrasso of Wyoming, the Republican Whip, Bill Cassidy of Louisiana and Thom Tillis of North Carolina. Both Barrasso and Cassidy are medical physicians.