Some of the doctors on the task force, including Dr. Anthony S. Fauci and Dr. Robert R. Redfield, were reluctant to show up in person at the White House, worried that the disdain there for mask wearing and social distancing would leave them at risk of infection.
Vice President Mike Pence was nominally in charge of the task force but was so cautious about getting crosswise with Mr. Trump as they battled for re-election that, in public at least, he became nearly invisible.
The debates inside the White House increasingly revolved around Dr. Atlas, who had no formal training in infectious diseases but whose views — which Mr. Trump saw him deliver on Fox News — appealed to the president’s belief that the crisis was overblown.
His arrival at 1600 Pennsylvania Avenue was itself something of a mystery. Some aides said he was discovered by Kayleigh McEnany, the White House press secretary. Others said John McEntee, the president’s personnel chief, had been Googling for a Trump-friendly doctor who would be loyal.
Marc Short, Mr. Pence’s chief of staff, opposed hiring Dr. Atlas. But once the president and his team brought him in, Mr. Short insisted that Dr. Atlas have a seat at the task force table, hoping to avoid having him become yet another internal — and destructive — critic.
Once inside, Dr. Atlas used the perch of a West Wing office to shape the response. During a meeting in early fall, Dr. Atlas asserted that college students were at no risk from the virus. We should let them go back to school, he said. It’s not a problem.
Dr. Birx exploded. What aspect of the fact that you can be asymptomatic and still spread it do you not understand? she demanded. You might not die, but you can give it to somebody who can die from it. She was livid.
“Your strategy is literally going to cost us lives,” she yelled at Dr. Atlas. She attacked Dr. Atlas’s ideas in daily emails she sent to senior officials. And she was mindful of a pact she had made with Dr. Hahn, Dr. Fauci and Dr. Redfield even before Dr. Atlas came on board: They would stick together if one of them was fired for doing what they considered the right thing.