As the president of the United States shelters in place with the White House press corps, and Joe Biden gibbers senselessly into the GoPro camera in his Delaware basement, this fall’s national election has been thrown into a cocked tricorn by the coronavirus. Many of Donald Trump’s retail-politicking strengths — the huge rallies, his command of crowds — have been neutralized, and while he still has control of the narrative from his bully pulpit in the West Wing, the national media remains dead set against him, and puts the worst possible spin on every word he speaks. Meanwhile, Biden and...