Mr. Trump will no doubt be frustrated that his campaign is confined to his personal residence or his office at Walter Reed hospital, but that may be an opportunity. Americans will be empathetic, and Mr. Trump can respond in kind. Ronald Reagan’s popularity soared after he was shot because he showed grace and cool under strain—“honey, I forgot to duck.” Rather than lash out at his critics, Mr. Trump can show optimism and fortitude and maybe even good humor in coping.

He could also use the time, and his virtual media appearances, to make a positive case for a second term. His strategy of attacking Mr. Biden and son Hunter personally isn’t working, so why not use fireside chats to frame the policy differences? He was headed for probable defeat before his new diagnosis, so he has little to lose by trying.

If Mr. Trump recovers soon, his example will underscore his larger campaign theme that America can return to a semblance of normal life and commerce despite the virus. He could, by the way he behaves when waylaid by Covid, set a positive example for the country.