President did not disclose 1st positive test, sources say

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.

President wants to leave hospital as soon as possible

Sources tell ABC News that President Trump was in good spirits Sunday, and was insisting that he wants to leave Walter Reed Medical Center as soon as possible.

Aides are pushing Trump to relax, sources say.

A timetable on Trump's release was still not finalized as of Sunday night, sources said. Doctors said earlier Sunday that Trump could leave the hospital as early as Monday.

-ABC News' Katherine Faulders and John Santucci

White House says 'appropriate precautions' taken for Trump's ride

The White House says President Trump's drive-by outside Walter Reed hospital Sunday evening was "safe to do," even as he fights the coronavirus.

Trump spokesman Judd Deere said "appropriate precautions" were taken for the short ride, giving little details other than PPE was used.

"The movement was cleared by the medical team as safe to do," Deere said in a statement.

However, infectious disease experts tell ABC News that the president is likely still infectious.

Dr. William Schaffner,  a professor of preventive medicine at Vanderbilt University, said, "You have to have been a certain number of days symptom-free, and 10 days from the onset of your illness -- or the date of positivity of your test."

"He's done something that no one would recommend," he told ABC News, saying that he may have put the Secret Service members who rode with him at risk.

"This did not appear to be an essential trip," Schaffner said.

-ABC News' Elizabeth Thomas, Sony Salzman and Sasha Pezenik

Biden tests negative

Vice President Joe Biden's campaign said he underwent PCR testing today and the results came back negative.

The campaign wouldn't provide more details about the test.

-ABC News' Molly Nagle

Barr is in self-quarantine, gets 3rd negative test result

Department of Justice spokeswoman Kerri Kupec told reporters that Attorney General Bill Barr is self-quarantining at home, but has so far tested negative for the virus.

The spokeswoman would not provide more details about Barr’s self-quarantine.

This is the third time he has tested negative for COVID-19 since last Tuesday's debate. Barr attended the Sept. 26 event at the White House where President Trump announced Judge Amy Coney Barrett as his Supreme Court Justice nominee.

Several Trump administration officials who contracted the virus last week, including Kellyanne Conway and former Gov. Chris Christie, attended the event and were not wearing masks during the outdoor ceremony.

Barr was photographed talking with Conway while not wearing a mask during the event.

-ABC News’ Alexander Mallin