In stump speeches made in January, Trump mentioned Sanders’s name — or, as Trump refers to him, “Crazy Bernie” — eight times as often as Biden.

Trump, if he wants to get serious about Sanders, may need to come up with a more effective nickname for the unorthodox independent senator from Vermont. “Crazy Bernie,” like Trump’s “Crazy Nancy” for House Speaker Nancy Pelosi, is the name Trump resorts to for political rivals he doesn’t know how to handle.