How Donald Trump turned America into a seething cauldron of political violence

The aftermath of the failed assassination attempt on Trump on July 13 was a rare moment in which voices across the spectrum pleaded: Political violence has no place in the United States.

There was one problem with the plea. For the last decade, the chief instigator, cheerleader, and apologist of political violence has been Donald J. Trump.

Trump revels in political violence. He alone fomented the deadly Jan. 6 insurrection, the only attempted coup in U.S. history. In 2017, he said...