WASHINGTON – President Donald Trump's doctors offered rosy assessments of his condition Sunday, but the few medical details they disclosed — including his fluctuating oxygen levels and a decision to begin treatment with a steroid drug — suggested to many infectious disease experts that he is suffering a more severe case of COVID-19 than the physicians are acknowledging.

In photos and videos released by the White House, there is hardly any sign that Trump is sick. But at a news conference at the Walter Reed National Military Medical Center in Bethesda, Md., Trump's doctors said his oxygen levels had dropped to a point that can indicate that a patient's lungs are compromised. The symptom is seen in many patients with severe COVID-19.

The president's medical team also said he had been prescribed dexamethasone on Saturday. The drug is a steroid used to head off an immune system overreaction that kills many COVID-19 patients.

The drug is reserved for those with severe illness, because it has not been shown to benefit those with milder forms of the disease and may even be risky.

Because of the incomplete picture offered by the president's doctors, it was not clear whether they had given him dexamethasone too quickly, or whether the president was far sicker than has been publicly acknowledged, experts in infectious disease and emergency medicine said Sunday.

"The dexamethasone is the most mystifying of the drugs we're seeing him being given at this point," said Dr. Thomas McGinn, physician-in-chief at Northwell Health, the largest health care provider in New York state. The drug is normally not used unless the patient's condition seems to be deteriorating, he added.

"Suddenly, they're throwing the kitchen sink at him," McGinn said. "It raises the question: Is he sicker than we're hearing, or are they being overly aggressive because he is the president, in a way that could be potentially harmful?"

Dr. Esther Choo, a professor of emergency medicine at Oregon Health & Science University in Portland, said of the doctors' statements Sunday: "This is no longer aspirationally positive. And it's much more than just an 'abundance of caution' kind of thing."

Some experts raised an additional possibility: that the president is directing his own care, and demanding intense treatment despite risks he may not fully understand. The pattern even has a name: VIP syndrome, which describes prominent figures who receive poor medical care because doctors are too zealous in treating them — or defer too readily to their instructions.

"You think you're helping," said Dr. Céline Gounder, a clinical assistant professor of medicine and infectious diseases at the NYU Grossman School of Medicine. "But this is really a data-free zone, and you just don't know that."

Still, based on the doctors' account, Trump's symptoms appear to have rapidly progressed since he announced early Friday morning that he had tested positive for the coronavirus.

Trump had a "high fever" Friday, and there were two occasions when his blood oxygen levels dropped, his doctors said — on Friday and again on Saturday. The president's oxygen saturation level was 93% at one point, his doctors said, below the 95% that is considered the lower limit of the normal range.

Many medical experts consider patients to have severe COVID-19 if their oxygen levels drop below 94%. The physicians said Trump had received supplemental oxygen at the White House on Friday; they were not clear about whether it had been administered again Saturday, or whether his blood oxygen levels had fallen below 90 at some point.

On Friday, Trump was given an infusion of an experimental antibody cocktail that is being tested in COVID-19 patients by the drugmaker Regeneron. Trump is also receiving a five-day course of remdesivir. The antibody cocktail fights the virus itself and may prevent it from spreading through the body. Remdesivir is commonly used with dexamethasone, which tamps down the body's immune response when some patients' immune systems go into overdrive and attack their vital organs.

For a coronavirus patient admitted Friday to be sent home Monday "would be remarkably atypical," said Robert Wachter, chairman of the University of California at San Francisco's department of medicine. "For someone sick enough to have required remdesivir and dexamethasone, I can't think of a situation in which a patient would be OK to leave on Day 3, even with the White House's medical capacity."

Wachter and other physicians said it sounds as if the president's lungs have been affected by the virus, based on his physicians' description Sunday that the president had episodes of low oxygen Friday and Saturday morning for which he was given supplemental oxygen to bring the levels up. "It confirmed what we all thought as we read between and around the lines yesterday," Wachter said. "He has a moderately serious case of COVID."