Just over a week after he began a rebooted effort, driven by rising infection rates and sinking poll numbers, to talk about the virus in terms more in line with medical consensus, Mr. Trump was again making unfounded claims and defending discredited medical experts. It was the sort of eccentric, science-deficient performance that many of his aides believe unnerved the public during the spring and has come to gravely threaten his re-election prospects.

Noting that Dr. Anthony S. Fauci, the government’s top infectious disease expert, and Dr. Deborah L. Birx, his administration’s top coronavirus coordinator, have high approval ratings even as his own have sagged, Mr. Trump added, “And yet, they’re highly thought of — but nobody likes me.”

“It can only be my personality,” he concluded.