Many presidents provoke personal animus beyond opposition to their policies. Ronald Reagan inspired angry punk songs. George W. Bush drove Democrats to distraction. (I still occasionally contribute to a Bush-era website called Smirking Chimp.) Bill Clinton and Barack Obama each evoked conspiracy theories on the far right.

Trump derangement syndrome is therefore familiar. But it’s also different in an important respect: While it’s epidemic among centrist Democrats, most progressives are immune.

“Re-electing...