Mr. Haidt has been studying political polarization for years, and what he’s seen in the data is distressing. Yet he would always say at the end of his talks that if present trends continue we’re in trouble, “but present trends never continue. Something will happen to force this off the trajectory.”

He thinks this might be “the thing”: “It’s the end of a cycle, not the end of the world.” He hopes that in a shift “from I to we,” Americans may more deeply cultivate the virtues we need as a democracy, “which include the virtues of the Christian and Jewish traditions—humility, mercy. We are so quick to judge. We need to be easier on each other, turn down the judgment 80% or 90%.”

“The virus may do this. We have all been humbled by it, as a nation of institutions and of individuals, from the beginning.”

That, by the way, is where Lincoln wound up at the end of the Civil War, thinking we must turn down the judgment. A friend this week quoted from Edward Achorn’s “Every Drop of Blood,” a study of Lincoln’s Second Inaugural Address. Mr. Achorn writes that Lincoln had come to think “it was time for Americans to stop thinking about self-righteousness. The only way forward was to recognize that all had been wrong and to treat each other with mercy.”