Trump's announcement of his diagnosis landed like a bombshell on Friday, some 48 hours after his first presidential debate with Democratic challenger Joe Biden, highlighting the uncertainty four weeks before the US election.
Doctors at Walter Reed National Military Medical Center in Bethesda, Maryland, are treating Trump, 74, with a steroid, dexamethasone, that is normally used only in the most severe cases. Trump was running a high fever on Friday and had been given supplemental oxygen after his blood oxygen levels dropped, Dr. Sean P. Conley, the White House physician, said on Sunday.
Conley was due to provide an update on the Republican president's condition at 3 p.m. EDT (1900 GMT), a White House official said.
Trump's medical team has painted a rosy picture of his condition despite the potentially fatal virus. White House Chief of Staff Mark Meadows told Fox News that he was optimistic Trump would be discharged on Monday.
Trump was reluctant to go to the hospital last week and is eager to get out, a source familiar with the situation told Reuters.
Even if discharged, Trump will need to undergo further treatment as part of a five-day course of an intravenous antiviral drug, remdesivir. The normal quarantine period for anyone testing positive for the novel coronavirus is 14 days.
Trump has for months played down the threat of the pandemic which has infected 7.4 million people in the United States and killed more than 209,000. In recent days, he released videos to reassure the public he is recovering from the disease caused by the virus.
The coronavirus outbreak around Trump widened on Monday when White House press secretary Kayleigh McEnany said she had tested positive for the virus after "testing negative consistently" every day since Thursday, the same day it was announced that White House aide Hope Hicks had tested positive.
McEnany, a well-known figure at the forefront of the White House's often combative dealings with the media, held a briefing for reporters on Thursday in which she did not wear a face mask.
Chad Gilmartin and Karoline Leavitt, who work in the White House's press office, also have tested positive, a source confirmed to Reuters.
"These people think this is all a game. Everyone in that White House who was exposed to Hope Hicks and the president should have begun quarantine last week. They don't care about the rules, which is why we have 200,000 dead. Vote them all out," Democratic Senator Chris Murphy tweeted.
TRAILING IN POLLS
A Reuters/Ipsos poll released on Sunday showed the Republican Trump trailing Biden, 77, nationally by 10 percentage points. About 65% of Americans said Trump would not have been infected had he taken the virus more seriously.
Trump has repeatedly flouted social-distancing guidelines meant to curb its spread. He also mocked former Vice President Biden at last Tuesday's debate for wearing a mask at events, even when he is far from other people.
Biden, who has tested negative for the disease several times since sharing the stage with Trump last week, said on Monday he was willing to participate in next week's scheduled presidential debate if health experts deemed it safe.
The Democratic White House hopeful was due to resume in-person campaigning on Monday in Florida, where polls showed a tight race in a crucial election battleground.
A return to the White House might help Trump project a sense of normalcy in his bid to win re-election on Nov. 3. Before falling ill, he had tried to pivot the campaign toward the U.S. economic recovery and the upcoming confirmation hearings for his Supreme Court nominee Amy Coney Barrett.
But the growing number of COVID-19 cases in the White House as well as Congress - three Republican senators have tested positive for the virus in the last week - threatens to draw further attention to Trump's pandemic response.
Vice President Mike Pence and his wife again tested negative for COVID-19 on Monday, an administration official said. Trump's chief of staff, Meadows, tested negative on Monday, an administration official said.
Pence is scheduled to debate Democratic vice presidential nominee Kamala Harris on Wednesday in Salt Lake City, Utah.
Trump's daughter, Ivanka Trump, and his son-in-law, Jared Kushner, who both work at the White House, also tested negative for the virus, Ivanka Trump's spokeswoman said. The president's wife, Melania, tested positive last week.
Trump is also under fire for a statement that he met with soldiers and first responders at the hospital in Bethesda, for going on a drive-by to greet supporters outside the facility on Sunday and for traveling to a fundraiser at his golf club in Bedminster, New Jersey, last Thursday. Critics said those actions potentially exposed even more people to the virus.
Major U.S. stock markets were trading higher on Monday amid hints of Trump's potential release and signs of progress with a new fiscal stimulus bill in Congress. Wall Street's main indexes slumped on Friday after Trump's COVID-19 announcement.
But doctors not involved in Trump's treatment said optimism about the president's condition might be misplaced. As an overweight, elderly man, Trump is in a category of people who are more likely to develop severe complications or die from the disease.