President Trump posted a new video to his Twitter account on Sunday saying that he is going to pay a "surprise visit" to supporters who have gathered outside of Walter Reed hospital, where he is being treated for COVID-19. He was spotted moments later in an SUV wearing a mask and waving to supporters.

Why it matters: The drive-by likely violates CDC guidelines, which call on health care professionals to "limit transport and movement of the patient outside of the room to medically essential purposes."

Behind the scenes: Trump has now returned to the presidential suite inside Walter Reed, according to a White House spokesperson. Reporters on pool duty at the hospital were not informed that Trump would be making the drive-by visit.

The state of play: This is the second video from Walter Reed that Trump has posted since his hospitalization. Earlier on Sunday, White House physician Sean Conley revealed that Trump experienced two "transient" episodes in which his oxygen saturation level dropped below 94% and that he received supplemental oxygen on Friday after registering a "high fever."

• Trump is now being treated with dexamethasone, a steroid that has been found to significantly reduce the risk of death among patients who are on a ventilator and provide more limited benefits for patients who are on supplemental oxygen.
• Overall, the president's condition has "continued to improve," Conley said.

What he's saying: "I want to thank them all — the nurses, the doctors everybody here. I've also gotten to meet some of the soldiers and first responders, and what a group," Trump said in a video posted at 5:16pm ET

• "I also think we're going to pay a little surprise to some of the great patriots that we have out on the street. They've been out there for a long time and they've got Trump flags and they love our country."
• "It’s been a very interesting journey," he continued. "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. And I understand it. And it’s a very interesting thing."

Of note: James Phillips, an attending physician at Walter Reed Medical Center, criticized Trump's drive-by, saying it put the lives of those inside the SUV "at risk for theater." "My thoughts are with the Secret Service forced to play," Phillips said.

• White House spokesperson Judd Deere told reporters, "Appropriate precautions were taken in the execution of this movement to protect the President and all those supporting it, including PPE. The movement was cleared by the medical team as safe to do."

pic.twitter.com/0Bm9W2u1x7

— Donald J. Trump (@realDonaldTrump) October 4, 2020

Trump drives by the press and supporters outside Walter Reed hospital. pic.twitter.com/3phtKthqTH

— Philip Crowther (@PhilipinDC) October 4, 2020

Editor's note: This article has been updated with new details throughout