His toxic relationship with Ms. Verma became so ugly and public last year that the two were summoned to the White House in December to determine whether they could continue to work together. Mr. Azar has also repeatedly clashed with Joe Grogan, the director of the White House’s Domestic Policy Council, who two senior administration officials said would soon leave his post. In recent weeks, several people close to the president grew even angrier with Mr. Azar for what they viewed as a public relations effort on his part to generate favorable coverage of his response to the virus at the president’s expense.

Now, Mr. Azar finds himself increasingly sidelined by Mr. Trump and his advisers, who blame the secretary for early failures on testing and for what they describe as inconsistent stewardship of the coronavirus task force in its first month…

Vice President Mike Pence took over for Mr. Azar as the leader of the task force at the end of February, and in the weeks since the episode at C.D.C. headquarters, Mr. Azar has been excluded from key coronavirus meetings, administration officials say, including one led by Mr. Grogan and another involving only the nation’s top medical officials.

“These are all arguably people who theoretically report to him, work for him, but like everything else, that has been upended in this administration, where it isn’t very clear if cabinet secretaries are choosing or even co-choosing their top political appointees,” said Kathleen Sebelius, a health and human services secretary under President Barack Obama. “I don’t have any idea how you operate in that environment when you’re excluded from meetings with your agency.”