Wearing a mask and surrounded by an extensive security detail - believed to be Secret Service agents - he waved to cheering fans from an armoured SUV motorcade - despite his doctor revealing he was on steroids for fluctuating oxygen levels.
A Walter Reed physician and the chief of disaster medicine at George Washington University, led a flood of criticism, with the president just three days into his Covid-19 infection.
"That presidential SUV is not only bulletproof, but hermetically sealed against chemical attack," Dr James Phillips said. "The risk of COVID-19 transmission inside is as high as it gets outside of medical procedures.
“The irresponsibility is astounding. My thoughts are with the Secret Service forced to play.
"Every single person in the vehicle during that completely unnecessary presidential 'drive-by' just now has to be quarantined for 14 days.
“They might get sick. They may die. For political theater. Commanded by Trump to put their lives at risk for theater. This is insanity."
Jonathan Reiner, professor of medicine and surgery at George Washington University, tweeted: "By taking a joy ride outside Walter Reed the president is placing his Secret Service detail at grave risk.
"In the hospital when we go into close contact with a Covid patient we dress in full PPE: Gown, gloves, N95, eye protection, hat. This is the height of irresponsibility.
"His doctors should have said no. They need to stand up for what is right. This is wrong."
Piers Morgan also weighed in, branding the drive-by "reprehensible" and "reckless".
The Good Morning Britain host raged: "What’s your reaction now you've had it yourself and learnt just how serious it is? You go out and you put your Secret Service lives at risk.
"People who risk their lives for you every minute of every day. You decide to get into a car with a bloke who's got a mask on who actually has to do that because the president told him."
He added: "He thinks it's a reality show. The recklessness of this. It’s utterly ridiculous."
White House spokesman Judd Deere said the drive had been “cleared by the medical team as safe” and that “appropriate precautions” were taken “including PPE”.
In his third video update since being diagnosed, Mr Trump said battling Covid’19 has “been a very interesting journey”.
He said: “I learned a lot about Covid. I learned it by really going to school. This is the real school. This isn’t the let’s read the books school. And I get it, and I understand it. And it’s a very interesting thing.”
Dr Sean Conley, the president’s physician, said Mr Trump had been on supplemental oxygen on Friday after his blood oxygen level plummeted twice.
The doctor added a new layer of confusion by suggesting he could be discharged and allowed to continue treatment at the White House on Monday, adding the president “has continued to improve”.
House Speaker Nancy Pelosi, who claimed she has been kept in the dark on the president’s condition, demanded honesty.
"We need to have trust that what they're telling us about the president's condition is real,” the Democrat told CBS.
Mrs Pelosi said the information doctors are giving the public “has to be approved by the president", adding: "That's not very scientific".
After the drive-by, reporters claimed a White House official told them First Lady Melania Trump would not leave her residence to visit her husband because: “That would expose the agents who would drive her there and the medical staff who would walk her up to him.”
The US election campaign was thrown into turmoil by the president’s diagnosis, with less than four weeks to go until polling day.