White House Chief of Staff Mark Meadows on Friday told Stephen Hahn, the commissioner of the Food and Drug Administration, to submit his resignation if the agency does not clear the nation’s first coronavirus vaccine by day’s end, according to people familiar with the situation who spoke on the condition of anonymity because they were not authorized to discuss what happened.

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!!!”

The warning led the FDA to accelerate its timetable for clearing America’s first vaccine from Saturday morning to later Friday.

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.”