Ms. Hicks, a longtime aide who is one of the president’s closest advisers, was more concerned, colleagues said. She took more precautions than most others and sometimes wore a mask in meetings.
Colleagues said that newcomers to Mr. Trump’s orbit, like Kayleigh McEnany, the White House press secretary, never wore a mask in his presence, in what was interpreted by other staff members as an attempt to please the new boss.
As the months progressed, there were so few reported virus cases in the White House — a valet to the president, a top aide to the vice president and Robert C. O’Brien, the national security adviser, all tested positive — that aides to the president grew even less concerned.
By June, the month before Mr. O’Brien tested positive, the White House had already stopped conducting temperature checks for people entering the complex. Only those aides who were interacting directly