The president had already tested positive Thursday when he appeared on Fox News.
President Donald Trump's condition is continuing to improve as he fights a coronavirus infection, doctors say, and he may be able to leave Walter Reed Medical Center as early as Monday -- even as details emerge that the president allegedly initially tested positive for COVID-19 earlier than he acknowledged.
Doctors also reported that Trump, over the course of exhibiting coronavirus symptoms, had earlier experienced two episodes of "transient drops" in his oxygen saturation.
Yet the president was feeling well enough Sunday evening to briefly leave Walter Reed for a surprise drive-by, waving to supporters outside the hospital.
Meanwhile, numerous questions remain about how many people at the highest levels of government had been exposed to the virus after a week of events involving the president where social distancing and mask-wearing were lax in the White House and elsewhere.
White House national security adviser Robert O'Brien while speaking to reporters at the White House on Sunday announced that mask wearing is now mandatory for National Security Council staff.
"We made mask wearing mandatory for National Security Council staff," O'Brien said.
Mask wearing was previously voluntary.
-ABC News' Elizabeth K. Thomas
Vice President Mike Pence and second lady Karen Pence again have been tested Sunday for the coronavirus and received negative test results, a White House official told ABC News.
This is the third day since President Donald Trump's coronavirus diagnosis that they have received a negative test result.
-ABC News' Elizabeth K. Thomas
House Speaker Nancy Pelosi, D-Calif., in an appearance on CBS's "Face the Nation" on Sunday, said she still hasn't heard from the president's team regarding his condition or any continuity of government matters.
"We're getting our information the way everyone else is: in the media. But in terms of the succession, that's an ongoing process. Sadly, at this time, it comes to the forefront," she said.
Amid calls to improve the testing system available to lawmakers and Capitol Hill denizens after this week, Pelosi said she has confidence in the recommendations of the Office of the Attending Physician of Congress -- noting that the sheer number of people working on the Hill (approximately 20,000 employees of all kinds) would pose a challenge for testing.
"There could be some sampling. Let’s depend on science on how deal with it," she said.
-ABC News' Benjamin Siegel
Doctors continue to plan to administer a five-day course of remdesivir to President Trump as part of his COVID-19 treatment.
The antiviral treatment has been shown to diminish recovery time in hospitalized coronavirus patients.
Due to two episodes of lower oxygen levels, the medical team treating the president is also now giving him the steroid dexamethasone, which he began to receive on Saturday.
President Trump's condition is said to be improving and doctors hope to discharge him back to the White House to continue treatment on Monday.
