We know how all of this is going to end: with Donald J. Trump.

I’m referring specifically to Jill Lepore’s “These Truths: A History of the United States,” though over the course of her hefty account of the American experience, one might begin to wonder about the fate of the republic itself.

Not that Lepore is one to stoke panic. Her one-volume history is elegant, readable, sobering; it extends a steadying hand when a breakneck news cycle lurches from one event to another, confounding minds and churning stomachs.

She writes in her introduction that “These Truths” “is meant to double as an old-fashioned civics book.” Just a few years ago, “an old-fashioned civics book” might have sounded like a cure for insomnia; now it sounds like a survival guide.

Lepore has the kind of credentials that verge on elite caricature — history professor at Harvard, staff writer at The New Yorker — but she grew up middle-class in Worcester, Mass., attended Tufts on an R.O.T.C. scholarship, and studied math before switching to English. Her mathematical background still finds expression in the precision of her work, despite its variousness. She has written about Wonder Woman and the Tea Party, to name just two of her many subjects; she has also been a finalist for the National Book Award and the Pulitzer Prize. ...