One post-election question is whether Democrats plan to treat defeat as an education in the limits of personal destruction as a political tool, and the early evidence isn’t promising. Witness the Chernobyl over Steve Bannon, who will be President-elect Trump’s “chief strategist” as liberals assail him as a white supremacist and anti-Semite.

Mr. Bannon is the former chairman of the incendiary Breitbart News website, as well as a Goldman Sachs alum, Navy veteran and early investor in “Seinfeld.” He kept a low profile at Donald...