But by the 1990s, greater numbers of the Republican Party’s grass-roots activists blamed declining standards of living not on the free market individualism they believed in almost religiously, but on job-taking immigrants and the shadowy machinations of the global elite. Such scapegoating is strikingly reminiscent of the radio priest Charles Coughlin’s attacks on the Rothschilds and “money-changers” during the Great Depression.

Mr. Trump championed ideas that had been bubbling up among the Republican grass roots since the late 20th century. His great political talent has been to see the extent of these resentments and rhetorically, and to some extent politically, speak to those concerns. His hold on his supporters is not just a cult of personality but grounded in a set of deeply rooted and increasingly widespread ideas within the Republican Party: ending birthright citizenship for immigrants, militarizing the border, disenfranchising Americans under the guise of protecting the integrity of the ballot, favoring an isolationist nationalism.

To put the full power of the nation’s chief executive behind such proposals was uniquely Trumpian, but the animating ideas have precedent in Republican politics.

There are no easy ways to quell this national rebellion, a rebellion that appears to be gaining velocity, but the first step has got to be organizing a political taxonomy that doesn’t marginalize them as aliens. 

The point here isn’t to sympathize with the rioters, or even seek to “understand” them, but to see them as they are and to prepare ourselves for future confrontations.

• various columnists