A doctor at Walter Reed Military Medical Centre, where the US president is being treated, said the move was "insanity".
ADVERTISEMENTDonald Trump has been criticised for taking a drive to wave at cheering supporters outside the hospital where he is being treated for coronavirus.
The US president, who was admitted to Walter Reed National Military Medical Center with COVID-19 just days ago, was spotted on Sunday in the back of an armoured SUV, wearing a mask and saluting the crowd.
In the front passenger seat and driving seat, Secret Service agents also wore masks and other protective gear.
"This is insanity," Dr James P Phillips, an attending physician at the hospital, said as he warned the president's trip could put lives at risk.
"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."
He added: "For political theatre. Commanded by Trump to put their lives at risk for theatre."
It comes as Trump's medical team earlier revealed their patient had received a second dose of experimental drug remdesivir along with a first dose of dexamethasone — a steroid often used to treat patients with a serious bout of the illness.
The doctors also said Trump's blood oxygen levels had twice dropped suddenly in the last few days, but assured he may still be discharged on Monday to continue treatment back at the White House.
In a video teasing his drive-by, Trump himself said it had been "a really interesting journey" as he quipped: "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 book' school. And I get it. I understand it.
"It's a very interesting thing, and I'm going to be letting you know about it.
"In the meantime, we love the USA, and we love what's happening."
The president, in what appeared to be an effort to show strength with just weeks to go before the election, also said he would "pay a little surprise" to those gathered outside the medical facility, applauding their "enthusiasm".
At 74 years old and with a morbidly obese BMI, Trump is considered to be at a higher risk of developing serious complications from COVID-19.
Therefore, confusion over the timeline of him announcing his diagnosis and the lack of basic medical information being released in briefings has brought further concern into view.
His doctor, Navy commander Sean Conley, has offered relatively cheerful updates on the president's condition, but admitted on Sunday that he was trying to reflect "the upbeat attitude" of the team.
Conley said he "didn’t want to give any information that might steer the course of illness in another direction."
"And in doing so, you know, it came off that we were trying to hide something, which wasn’t necessarily true. The fact of the matter is that he’s doing really well," he added.
ADVERTISEMENTConley had spent much of the briefing dodging reporters' questions as he was pressed to reveal exactly when Trump's oxygen levels had dropped — something that hadn't been mentioned in previous announcements. He also refused to answer whether lung scans showed signs of damage.
"There’s (sic) some expected findings, but nothing of any major clinical concern," he said, but did not reveal what the "expected findings" were.
Trump's oxygen level at the time of the briefing was said to be at 98% — a normal reading.
Natasha Lindstaedt is a professor in the Department of Government at the University of Essex. She says the White House response to the situation has been chaotic:
"The Trump Administration is handling it the way it handles everything: it likes to sow confusion, it isn't transparent, it isn't fully telling the truth about this. But medical experts are saying this doesn't make sense, the timeline doesn't make sense, it doesn't make sense that he'd be released from hospital so soon."
ADVERTISEMENTMeanwhile, political rival Joe Biden, who has been more cautious in his approach to the virus, tested negative again on Sunday — it comes after his 90-minute appearance alongside the president at last week's election debate.
Contacts of Trump test positive for virus
First Lady Melania Trump is still currently quarantining at the White House, where she is overcoming her own bout of the illness.
White House Press Secretary Kayleigh McEnany announced she tested positive on Monday despite "experiencing no symptoms".
She last held a press briefing on October 1 but said that "no reporters, producers, or members of the press are listed as close contacts by the White House Medical Unit."
"With my recent positive test, I will begin the quarantine process and will continue to work on behalf of the American People remotely," she added.
ADVERTISEMENTAt least three journalists who cover the White House have also tested positive for the virus, the White House Correspondents' Association said.
Several people who attended the nomination ceremony for Judge Amy Coney Barrett have also tested positive including two senators, Trump's former advisor Kellyanne Conway and former NJ governor Chris Christie.
Guidelines from the Centers for Disease Control and Prevention (CDC) stipulate that transport or movement of a patient with COVID-19 should be "limited to medically essential purposes".
White House spokesman Judd Deere insisted the trip was "cleared by the medical team as safe to do," and added that extra precautions had been taken.
Watch an interview with Natasha Lindstaedt, in the media player above.
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