The top Republican on the Senate’s chief health committee, Sen. Bill Cassidy, R-La., indicated Thursday during Robert F. Kennedy Jr.'s second confirmation hearing of the week that his vote for Trump’s nominee to head Health and Human Services was not a lock, noting that he was “struggling” to confirm Kennedy over his inability to admit vaccines are safe and don’t cause autism.

Kennedy faced two separate hearings in front of Senate lawmakers this week in his bid to be the next secretary of the Department of Health and Human Services. Kennedy was probed frequently over his views on vaccines, which have been a sticking point for many senators as they figure out whether to vote in favor of Kennedy’s nomination or not.

During the hearings, Kennedy refused to reject claims he has posited publicly in the past that vaccines cause autism and argued he is not anti-vaccine but rather “pro-safety.” Kennedy added during the hearings that his plan as HHS secretary would be to “follow the science,” noting that if the science says he is wrong on vaccines, he will publicly apologize.

But senators, like Cassidy, have suggested during Kennedy’s confirmation hearings that the science says vaccines are safe — and they don’t cause autism.

“My responsibility is to learn, try and determine, if you can be trusted to support the best public health,” Cassidy, a former physician, said during his closing remarks at Kennedy’s Thursday confirmation hearing in front of the Senate Committee on Health, Education, Labor and Pensions (HELP). “A worthy movement called ‘MAHA,’” Cassidy continued, “to improve the health of Americans, or to undermine it, always asking for more evidence, and never accepting the evidence that is there … That is why I’ve been struggling with your nomination.”