The person most capable of defeating Donald Trump is Donald Trump. If Democrats are smart, they will let him do the job.

President Trump thrives on outrage and resentment. He seethes with it, stirs it in others and mines it for his own political profit. His political project relies on driving Americans to their cultural and ideological corners. He is Pavlov. We are the dogs.

Mr. Trump’s serial assaults on the decency and the decorum upon which civil society depends are enraging — and meant to be. It is only natural to respond to his every provocation with righteous indignation.

My advice to the Democratic nominee next year is: Donʼt play.