President Donald Trump on Sunday briefly left his hospital room at Walter Reed National Military Medical Center, where he is being treated for Covid-19, to drive past a group of supporters, a move medical experts and Democrats swiftly criticized as "insanity."

He is among others being accused of putting the lives of Secret Service personnel in danger by exposing them to the virus.

The president posted a video to his Twitter account around 5:15 p.m. announcing that he would "pay a little surprise to some of the great patriots that we have out on the street."

A few minutes later, the presidential motorcade slowly drove by the perimeter of the hospital, where a crowd had been gathering since Friday night. Trump was seen through the window of an SUV waving and wearing what appeared to be a cloth mask, as opposed to a more protective N95 mask.

The president does not travel anywhere without Secret Service protection, and Sunday's drive was no exception. At least two other people can be seen in the car with Trump.

First lady Melania Trump, who also has Covid-19, would not leave isolation in the White House residence to visit her husband at the hospital, a White House official said Saturday.

"She has Covid," the official said. "That would expose the agents who would drive her there and the medical staff who would walk her up to him."

The unannounced trip sparked backlash from several prominent Democratic lawmakers and some doctors not involved in his care, who accused Trump of unnecessarily putting Secret Service agents at risk.

Dr. James Phillips, an attending physician at Walter Reed, tweeted that the "Presidential SUV is not only bulletproof, but hermetically sealed against chemical attack," and that therefore the risk of Covid-19 transmission was "as high as it gets outside of medical procedures."

"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," he added.

Dr. Esther Choo, an emergency room physician and professor at Oregon Health and Science University, told MSNBC: "It makes me sick to see him in close quarters with others in that car."

Dr. Céline Gounder, an infectious disease expert and professor at New York University, accused Trump of "putting the health of others at risk."

Rep. Bill Pascrell Jr., D-N.J., called the event "a goddamn disgrace" on Twitter.

"To bask in the adulation of a handful of his supporters, trump just endangered the lives of Secret Service agents and others in his entourage," he added.

Rep. Eric Swalwell, D-Calif., tweeted: "It is criminal negligence for @realDonaldTrump to recklessly expose others. Pray for the Secret Service."