President Donald Trump said Wednesday that the White House may not approve tougher FDA guidelines for authorizing the emergency use of any coronavirus vaccines.

“That has to be approved by the White House,” Trump said. “We may or may not approve it.”

Trump also suggested that the FDA’s decision to revise the standards, first issued in June, “was a political move more than anything else.” The president has repeatedly vowed that a vaccine would be available by Election Day, although prominent scientists within his administration have said it’s extremely unlikely.

The stricter FDA standards cleared a review by the Department of Health and Human Services on Tuesday, with the expectation that the White House would soon approve them, according to two people with knowledge of the timeline.

Trump’s remarks came hours after he spoke with HHS Secretary Alex Azar about the FDA proposal, two people familiar with the situation said. The president’s criticism throws into jeopardy an effort viewed as key to boosting public confidence in any eventual coronavirus vaccine.

The White House, HHS and FDA declined to comment on Azar’s conversation with Trump.

Four vaccines are now in the final stage of clinical trials in the United States — studies that are designed to determine whether any of the shots are effective at preventing coronavirus infections.

Trump’s repeated promises that a vaccine is imminent contradict top government health officials who say that a shot won’t be ready until late 2020 at the earliest, and that it will take months longer to get it to all Americans. The president’s hard charge for a vaccine has prompted fears that his administration will rubber-stamp a shot based on political calculations rather than scientific data.

Faced with a steady stream of polls showing shrinking public confidence in the coronavirus vaccine race, FDA Commissioner Stephen Hahn has sought to reassure Americans that any shot his agency greenlights will be safe and effective.

“I will fight for science,” Hahn told a Senate committee on Wednesday morning. “I will fight for the integrity of the agency, and I will put the interests of the American people before anything else.”

He told senators that “FDA will not authorize or approve a vaccine we won’t be confident in giving to our families.”

Hahn said last week that his agency would be issuing the tougher emergency-use guidance for coronavirus vaccines, although that updated advice has not been made public.