WASHINGTON — President Trump made a rare appearance in the Situation Room on Sunday as his pandemic task force was meeting, determined to talk about the anti-malaria medicine that he has aggressively promoted lately as a treatment for the coronavirus.

Once again, according to a person briefed on the session, the experts warned against overselling a drug yet to be proved a safe remedy, particularly for heart patients. “Yes, the heart stuff,” Mr. Trump acknowledged. Then he headed out to the cameras to promote it anyway. “So what do I know?” he conceded to reporters at his daily briefing. “I’m not a doctor. But I have common sense.”

Day after day, the salesman turned president has encouraged coronavirus patients to try hydroxychloroquine with all of the enthusiasm of a real estate developer. The passing reference he makes to the possible dangers is usually overwhelmed by the full-throated endorsement. “What do you have to lose?” he asked five times on Sunday.

Bolstered by his trade adviser, a television doctor, Larry Ellison of Oracle and Rudolph W. Giuliani, a former New York mayor, Mr. Trump has seized on the drug as a miracle cure for the virus that has killed thousands and paralyzed American life. Along the way, he has prompted an international debate about a drug that many doctors in New York and elsewhere have been trying in desperation even without conclusive scientific studies.