And the fraying of the social contract is getting worse. Americans express less and less trust in many institutions. Substantial majorities of people say that government, business leaders and the media are purposefully misleading them. In striking contrast to older generations, majorities of younger people say they do not believe that “the American dream” is achievable anymore. The health insurance industry likes to cite polls that show overall satisfaction, but those numbers go down when people get sick and learn what their insurer is and is not willing to do for them.

Things are much better now than in the 19th century. But there is a similarity to the trajectory and the mood, to the expression of deep powerlessness and alienation.

Now, however, the country is awash in powerful guns. And some of the new technologies that will be deployed to help preserve order can cut both ways. Thompson’s killer apparently knew exactly where to find his target and at exactly what time. No evidence has emerged that he had access to digital tracking data, but that information is out there on the market. How long before easily built artificial-intelligence-powered drones equipped with facial recognition cameras, rather than hooded men with backpacks, seek targets in cities and towns?