In the late winter of 1815, Thomas Jefferson sat down in his study at Monticello to work out a math problem.

Under Virginia law, a person with a black ancestor had to have at least seven-eighths white ancestry to count as a fully legal citizen. Jefferson was trying to figure out how many generations it would take — and whether his children with Sally Hemings, his mixed-race slave, would make the cut. He decided they did.

That absurd calculation — by the same man who justified his nation’s independence on the basis that “all men are created equal” — is one of many ironies Jill Lepore notes on her absorbing journey through U.S. history in “These Truths,” a title taken from a Jeffersonian clause in that same declaration.

Lepore, a Harvard University history professor known for her lucid New Yorker essays on American life and culture, dives into the cross-grained American epic starting with Christopher Columbus in 1492 and ending with Donald Trump in 2016.

That story, she writes, essentially is the working out of a question that the founders raised in the 1700s and every generation since has struggled to answer: Can a people rule themselves “by reflection and election, by reason and truth, rather than by accident and violence, by prejudice and deceit?”

Lepore’s history shows the answer is yes, they can — but be prepared for some backsliding. If the current national divisiveness is troubling, it’s not unprecedented. Slavery, civil war, Jim Crow, depression, blacklists, undeclared wars: It’s been a bumpy ride.

In the past few decades, thick American surveys have hit the shelves ranging from Howard Zinn’s 1980 radical history to Paul Johnson’s buoyant, libertarian 1997 volume. Lepore’s book is neither as glibly optimistic nor as comprehensive as Johnson’s; if you’re looking to find out about the Gadsden Purchase, Custer’s Last Stand or the Wright Brothers, you won’t find it here.

Instead, “These Truths” is primarily a political history that focuses on the expansion (and contraction) of rights in the United States — speech, religion, voting, even gun rights — along with political equality and popular sovereignty. And while Lepore pays due deference to the Mount Rushmore-sized figures who have wrestled with those ideas, her protagonists make up a more diverse crowd than those in most histories.

So we have Mary Lease, a fiery Kansas populist who wrote and lectured on behalf of farmers and laborers; journalist Walter Lippmann, who inspired Woodrow Wilson’s Fourteen Points and warned that mass communication gave the power of public persuasion to a limited few; Clem Whitaker and Leone Baxter, who changed campaigns forever when they pioneered political consulting in the 1930s and blocked Harry Truman’s national health insurance plan; and Phyllis Schlafly, the conservative activist whose work against abortion and the Equal Rights Amendment, Lepore writes, led to the Reagan Revolution of the 1980s — and whose last public act was endorsing Trump in 2016.

If the book has a moral conscience, it would be that of Frederick Douglass, the African-American reformer whose abolitionist and civil rights campaigns occupy a large chunk of the middle of the book. Proof that those issues still live is Lepore’s mention of Philando Castile, the St. Paul man whose 2016 shooting death in Falcon Heights by police was livestreamed by his girlfriend.

At more than 900 pages, this is a big book. But it’s a big subject, and Lepore is as graceful and witty a writer as anyone who has tackled it. Chapter after chapter, she offers new ways to think about familiar topics; for instance, she points out that the expansion of the press usually heralded a change in political parties, and she notes that most Americans first became investors when the federal government sold bonds to finance World War I.

To be sure, the book tilts liberal. But Lepore is nowhere close to being predictable in her judgments. She traces the modern welfare system not to FDR but to Southern women who petitioned the Confederate government for relief during the Civil War, and she credits Bill Clinton and his affair with Monica Lewinsky with giving Donald Trump his first political platform. The right to own a gun picked up steam in the 1960s not because of the NRA, she says, but because of black nationalists such as Malcolm X.

“Some American history books fail to criticize the United States; others do nothing but. This book is neither kind,” Lepore writes. “The truths on which the nation was founded are not mysteries, articles of faith, never to be questioned … but neither are they lies, all facts fictions, as if nothing can be known.”

John Adams famously said: “Facts are stubborn things.” But at a time when even facts are under assault, it’s bracing to be reminded by this remarkable book that with “all its hopes and all its boasts,” as John F. Kennedy said, the Great Republic and its progression through its third century remain best measured against the truths that gave it life from the very start.

 Kevin Duchschere is a team leader at the Star Tribune. 612-673-4455

These Truths
By: Jill Lepore.
Publisher: W.W. Norton, 932 pages, $39.95.