Rod Nelson, 65, a lifelong Republican and the retired C.E.O. of the Mackinac Straits Health System, said he had been “astonished” at the lack of leadership in handling the coronavirus crisis from Mr. Trump, a man he voted for in 2016, but won’t again in 2020.

Mr. Nelson’s son lives in Taiwan and while visiting there in January, his son’s in-laws told him they believed the coronavirus, then reported to be a few thousand cases largely limited to China, was more extensive than that. They were seeing at the time “smoke constantly coming from the crematoriums.” If he and his relatives knew it was going to get bad, he noted, “certainly the U.S. knew.”

“If Trump had just worn that damn mask from the beginning, his supporters would have too,” he said.