The threat came on the same day that President Trump tweeted that the FDA is “a big, old, slow turtle” in its handling of vaccines, while exhorting Commissioner Stephen Hahn to “get the dam vaccines out NOW.” He added: “Stop playing games and start saving lives!!!”

It also led the FDA to accelerate its timetable for clearing America’s first vaccine from Saturday morning to later Friday, according to two people familiar with the process who spoke on the condition of anonymity to discuss internal matters.

The White House actions once again inject politics into the vaccine race, potentially undermining public trust in one of the most crucial tools to end the pandemic that has killed more than 290,000 Americans. It comes in the midst of a process that had been designed to show no shortcuts were taken in reviewing the safety and effectiveness of a vaccine as surveys show many people remain unsure whether they will get the shots.

A White House official declined to comment, saying “we don’t comment on private conversations, but the Chief regularly requests updates on progress toward a vaccine.”

“This is an untrue representation of the phone call with the Chief of Staff,” Hahn said in a statement. “The FDA was encouraged to continue working expeditiously on Pfizer-BioNTech’s EUA request. FDA is committed to issuing this authorization quickly, as we noted in our statement this morning.”

The two-shot vaccine, which has been shown to be 95 percent effective in randomized trials involving tens of thousands of people, has already been cleared by Britain, Canada, Bahrain and Saudi Arabia. U.S. officials have engaged in a more rigorous review process that they believe will boost public confidence.

Meadows’ threat and the president’s tweets constituted the latest attack by Trump, who has complained vociferously that the vaccine wasn’t authorized before Election Day, blaming it on the ‘Deep State’ inside the agency that he accused of working against his reelection. Trump was also said to be upset that Britain cleared the vaccine before the United States, although the Pfizer-BioNTech vaccine has been developed and reviewed in record time.

An FDA statement issued early Friday morning said the FDA had informed Pfizer that it would “rapidly work toward finalization and issuance of an emergency use authorization” following Thursday’s endorsement of the Pfizer-BioNTech vaccine by an agency advisory committee.

The statement was signed by Hahn and Peter Marks, director of the Center for Biologics Evaluation and Research, which reviews vaccines. The officials said the FDA has also notified the Centers for Disease Control and Prevention and Operation Warp Speed, “so they can execute their plans for timely vaccine distribution.”

An FDA advisory committee reviewed the vaccine for more than eight hours Thursday and voted overwhelmingly in favor of using it in people age 16 and up.