Trump (74) was captured on video waving from the back seat of a black SUV on Sunday evening wearing a mask, as crowds cheered and waved American flags and pro-Trump banners outside Walter Reed National Military Medical Center in the Washington suburb of Bethesda, Maryland.
Two people could be seen in the vehicle's front seats.
Patients who test positive for Covid-19 are generally required to quarantine for 14 days, the typical incubation period for the coronavirus to avoid infecting others. The disease has killed more than 200,000 Americans.
Trump tested positive on Thursday and did not disclose his infection until the early hours of Friday morning.
Shortly before the brief ride, Trump posted a video on Twitter saying he would "pay a little surprise to the some of the great patriots we have out on the street."
White House spokesman Judd Deere described the drive as a "short, last-minute motorcade ride to wave to his supporters" and said Trump quickly returned to his hospital suite.
Deere said "appropriate precautions were taken" before the ride to protect the President and those supporting him. "The movement was cleared by the medical team as safe to do," he said.
Criticism of the ride was swift, including from an attending physician at Walter Reed.
"Every single person in the vehicle during that completely unnecessary Presidential 'drive-by' just now has to be quarantined for 14 days," James Phillips, who is also an assistant professor of emergency medicine at George Washington University's medical school said on Twitter.
"They might get sick. They may die. For political theatre."
Senator Brian Schatz, a Hawaii Democrat, added that he was praying for the health of Trump's Secret Service security detail: "They understood the risk inherent in the job, but they shouldn't have to contemplate that the risk is coming from the protectee."
The White House Correspondents Association issued a statement saying it was "outrageous" that Trump left the hospital without a press pool present. "The American public deserves independent coverage of the president so they can be reliably informed about his health."
There were some messages of support. Texas Governor Greg Abbott, a Republican, reacted to news of the motorcade by tweeting: "Looks like @realDonaldTrump is making a swift recovery from COVID. So many prayers answered."
Doctors treating Trump for Covid-19 are monitoring the condition of his lungs after he received supplemental oxygen, hours before he surprised supporters outside the hospital by riding past in a motorcade.
Trump has taken two doses of a five-day course of the intravenous antiviral drug Remdesivir, his doctors said at a briefing on Sunday morning, as well as the steroid dexamethasone, which is used in severe cases.
He has taken two doses of a five-day course of the intravenous antiviral drug Remdesivir, as well as the steroid dexamethasone, which is used in critical cases.
Dr Sean P Conley acknowledged that Trump's blood oxygen levels had dropped in prior days and that he had run a high fever on Friday morning, admitting that the president's condition had been worse than previously disclosed. Conley said Trump was improving on Sunday.
The briefing came the day after contradictory messages from the White House caused widespread confusion about the president's condition.
Trump spent much of the year downplaying the risks of the Covid-19 pandemic, which has infected 7.4 million Americans, killed more than 209,000, and caused an economic downturn that has thrown millions out of work.
His illness has upended his re-election campaign as it seeks to fend off Democratic challenger Joe Biden (77) in the final month of the race, and rattled financial markets. Several members of his inner circle have also tested positive for the disease, including three Republican members of the US Senate.
Two members of the White House residence staff tested positive for Covid-19 a few weeks ago, and Trump's "body man" aide Nicholas Luna has also tested positive, according to a source familiar with the situation.
Asked what tests had revealed about the condition of Trump's lungs, Conley replied, "There's some expected findings, but nothing of any major clinical concern."
Conley's response suggests the X-rays revealed some signs of pneumonia, said Dr Amesh Adalja, an infectious disease specialist at Johns Hopkins University.
"The expected finding is that he has evidence of pneumonia in the X-ray. If it was normal they would just say it is normal," Adalja said.
Doctors said the president had a high fever on Friday morning but has not run a fever since Friday.
Dr Brian Garibaldi said Trump was given the steroid dexamethasone in response to "transient low oxygen levels."
"He received his first dose of that yesterday and our plan is to continue that for the time being," Garibaldi said.
Dexamethasone is shown in studies to improve survival for patients hospitalised with critical Covid-19 who need extra oxygen. But it should not be given in mild cases since it can limit the body's own ability to combat the virus, according to guidelines from the Infectious Disease Society of America.
Trump is also being given an experimental treatment, Regeneron's REGN-COV2, as well as zinc, Vitamin D, famotidine, melatonin and aspirin, his doctors have said.
"Our plan for today is to have him eat and drink, be up out of bed as much as possible, to be mobile," Garibaldi said.
Trump released a four-minute video on Saturday in which he said the "real test" of his condition will come over the next few days.
"Over the next period of a few days, I guess that's the real test, so we'll be seeing what happens over those next couple of days," Trump said into the camera, looking tired and wearing a jacket and open-necked shirt. He tweeted thanks to his supporters on Sunday.
Differing assessments of Trump's health from administration officials on Saturday left it unclear how ill the president had become since he tested positive for the coronavirus on Thursday night.
Conley commented on the contradictory assessments on Sunday.
"I was trying to reflect an upbeat attitude of the team and the president about the course his illness has had," Conley told reporters on Sunday.
"I didn't want to give any information that might steer the course of illness in another direction and in doing so, it came off that we were trying to hide something, which isn't necessarily true."
'AGGRESSIVE' CAMPAIGN CONTINUES
A Reuters/Ipsos poll published on Sunday found Biden had opened a 10 point lead over Trump nationally, slightly wider than it has been for the past two months.
Some 65% of Americans said Trump likely would not have been infected had he taken the virus more seriously - a view that half of registered Republicans polled supported. Some 55% said they did not believe Trump had been telling the truth about the virus.
Trump's campaign vowed that Vice President Mike Pence, who would assume the presidency if Trump were unable to carry out his duties, would have an "aggressive" campaign schedule this week, as would Trump's three oldest children.
"We can't stay in our basement or shut down the economy indefinitely. We have to take it head-on," Trump campaign senior adviser Jason Miller said on ABC's This Week on Sunday.
Pence, who tested negative on Friday, is scheduled to debate Democratic vice presidential nominee Kamala Harris on Wednesday.
Biden, who largely avoided direct criticism of Trump during a campaign trip to Michigan on Friday, took a more aggressive tone on Saturday while speaking to a transit workers' union, even as he wished the president well.
"I'm in a little bit of a spot here, because I don't want to be attacking the president and the first lady now," Biden said, adding he hoped Trump and his wife Melania, who also has the illness, make a full recovery.
But he quickly turned to Trump's response to the pandemic, calling it "unconscionable" and blasting Trump's comment in an interview this summer that "it is what it is" when asked about the death toll.
Biden, who tested negative on Friday, told reporters he would next be tested on Sunday. His campaign will begin releasing the results of each test, a spokesman said.
Related Stories
Comments
Even when he is sick in hospital, the media has to treat it as a "gotcha" opportunity...
He wasn't in the hospital though, was he, he was out in public.
Anyone who believes anything said by tRump and his minions is ultra-gullible.
Why is he even in hospital? The virus, according to him, is a hoax, it's as real as his bone-spurs. If he was true to his word he would have kept playing golf and ignoring his job as usual, and not gone to hospital. But of course, it's all lies and the coward rushes to hospital as soon as his nose runs a little.
That and continuously pointing out he is trailing in the polls, biden's in the lead etc etc, typical meda though, all bought and paid for.
Yeah, who would ever politicise Covid?