On Saturday, Conley said Trump's blood oxygen level was 96%, which is in the normal range. The two experimental drugs he has received, given through an IV, have shown some promise against COVID-19. On Friday, he was given a single dose of a drug Regeneron Pharmaceuticals Inc. is testing to supply antibodies to help his immune system fight the virus.

Friday night, he began a five-day course of remdesivir, a Gilead Sciences drug currently used for moderately and severely ill patients. The drugs work in different ways — the antibodies help the immune system rid the body of virus and remdesivir curbs the virus' ability to multiply.

"We're maximizing all aspects of his care," attacking the virus in multiple ways, Conley said. "I didn't want to hold anything back if there was any possibility it would add value to his care."

He noted that in many cases, COVID-19 can become more dangerous as the body responds. "The first week of COVID, and in particular day seven to 10, are the most critical in determining the likely course of this illness," he said.

At the same time, the White House has been working to trace a flurry of new infections of close Trump aides and allies. Attention is focused in particular on last Saturday's White House event introducing Trump's Supreme Court nominee. That day, Trump gathered more than 150 people in the Rose Garden, where they mingled, hugged and shook hands — overwhelmingly without masks. There were also several indoor receptions, where Trump's Supreme Court pick, Judge Amy Coney Barrett, her family, senators and others spent time in the close quarters of the White House, photographs show.

Among those who attended and have now tested positive: former New Jersey Gov. Chris Christie, White House counselor Kellyanne Conway, the president of the University of Notre Dame, and at least two Republican lawmakers — Utah Sen. Mike Lee and North Carolina Sen. Thom Tillis. The president's campaign manager, Bill Stepien, and the head of the Republican National Committee, Ronna McDaniel, have also tested positive, though they were not at the event.