Experts said resuming a public schedule might worsen Mr. Trump’s condition, which could still rapidly deteriorate in the next several days. Covid-19, an unpredictable disease, can suddenly and unexpectedly worsen during a patient’s second week of illness. Based on the information provided, “No, I would not clear him to start public engagements on Saturday,” said Dr. Phyllis Tien, an infectious disease physician at the University of California, San Francisco, where she conducts and advises on Covid-19 clinical trials.

White House aides privately expressed concern about whether the president’s animated mood in recent days stemmed from the dexamethasone. Doctors not involved with the president’s care said it could have a significant effect on a patient’s behavior.

Dr. Negin Hajizadeh, a pulmonary/critical care physician at Northwell Health, noted that the majority of Covid patients receiving dexamethasone are on mechanical ventilation and in a state of induced coma, so they do not exhibit any behavioral side effects. But, she said, large studies show that generally 28 to 30 percent of patients will exhibit mild to moderate psychiatric side effects like anxiety, insomnia, mania or delirium after receiving steroid treatments, and about 6 percent may develop psychosis.