SCRANTON, Pennsylvania — As we spoke in the living room of his modest home just outside Scranton, Ralph Mercuri listed the problems afflicting America: the never-ending plague, deepening political tribalism, the looming prospect of another Trump presidential run.

But what distressed him most was unexpected: his belief that Joe Biden is no longer up to the job of being president. “This physical thing has really shaken me,” Mercuri said, his voice growing unsettled and his face flushing red. “He just looks frail, physically. He scares me right now. And he’s more forgetful now and more rigid in his thinking.”