Former Centers for Disease Control and Prevention Director Susan Monarez testified before senators on Wednesday that Health Secretary Robert F. Kennedy Jr. fired her after she refused to endorse forthcoming vaccine recommendations without reviewing scientific evidence to support the guidance.

Monarez was ousted just 29 days into the job, over disagreement with her boss on vaccine policies.

Republican Sen. Bill Cassidy, who chairs the powerful health committee Monarez is appearing before, expressed skepticism over the explanations Kennedy has given over her firing. He carefully praised President Donald Trump for his commitment to promoting health among Americans but made it clear he was befuddled by Monarez's removal.

Monarez said in her testimony that Kennedy gave her an ultimatum: “Preapprove” new vaccine recommendations from an advisory CDC panel that Kennedy has stocked with some medical experts who doubt vaccine safety or be fired. That panel is expected to vote on new vaccine recommendations later this week. He also demanded Monarez fire high-ranking, career CDC officials without cause, she said.

“He said if I was unwilling to do both, I should resign. I responded that I could not preapprove recommendations without reviewing the evidence, and I had no basis for firing," Monarez told senators. “He said he had already spoken with the White House several times.”