Extremism has been present in America for a long time. But Trump is applying a match to the kindling.

Trump calls Democrats “evil” and “crazy.” He accuses them of being “treasonous” and “un-American.” He claims they are in league with MS-13 gang members. He says they are trying to open our borders to criminals and to turn America into Venezuela — a bankrupt socialist dictatorship. He denounces the media as “the enemy of the people.” He applauds a congressman who assaulted a reporter and calls for his political opponent to be locked up. He singles out minorities such as Waters for opprobrium, and he promotes anti-Semitic conspiracy theories that hold George Soros responsible for everything from the Central American caravan to protests against Brett M. Kavanaugh.

When Trump talks about “globalists,” the far right hears “Jews.” When Trump says there were “fine people” on both sides in Charlottesville, the far right hears official approval. There is so much anti-Semitic filth online now. I see it every day on Twitter and in my email inbox. Normally I tune it out. Just background noise. But others are listening.