“If people were given the choice between democracy and whiteness, how many would choose whiteness?”

Taylor Branch, the Pulitzer Prize-winning historian of the Civil Rights Movement, drops that question like a bomb on Page 352 of “Caste,” the new book by Isabel Wilkerson, herself also a winner of Joseph Pulitzer’s prestigious prize. There are many moments in “Caste” that bring you up short in the starkness of their truth. But none hits quite as hard as that one, nor cuts quite as close to the bone of American fears.

“Caste” is the follow-up to 2010’s “The Warmth of Other Suns,” a history of The Great Migration, the mass exodus in which 6 million African Americans left the South in search of America. If anything, Wilkerson, a former reporter for The New York Times, is even more ambitious in her new book. “Caste” seeks nothing less than to reframe our understanding of America’s original sin.

What bedevils us, she argues, is not merely “racism,” a word that rarely appears in the book’s nearly 400 pages. Race, after all, is “fluid and superficial, subject to periodic redefinition,” as seen in the fact that Irish, Jewish and Armenian Americans like Conan O’Brien, Ruth Bader Ginsburg and Kim Kardashian are uniformly considered “white,” a status their forebears would have been enthusiastically denied.

But caste, the stratification of humanity into desirables, undesirables and those in-between, is “fixed and rigid.” And in America, “black” people, whether blonde and blue-eyed like former NAACP chief Walter White, or dark of hair and skin like actor Sterling K. Brown, are always at the bottom of that hierarchy.

“Caste is the bones, race the skin,” writes Wilkerson. Which is to say, it is the excuse, the justification.

Germany in the 1930s, she reminds us, was a caste system; in fact, the Nazis modeled their oppression of the Jews on America’s Jim Crow laws, which they greatly admired. India still maintains a complex caste system. On a 1959 visit, Martin Luther King was initially “a bit shocked and peeved” to hear himself introduced to a group from the lowest caste as “a fellow untouchable.” It took him some time to recognize the truth in what he’d heard. Like every other “Negro,” he later wrote, “I am an untouchable.”

Wilkerson’s book arrives at a time when it is sorely needed. It’s not just that we are seeing democracy stolen before our eyes, the postal service under assault, polling places closed, voter rolls purged, Donald Trump openly flirting with ignoring election results — not just the fact of it all, but the why of it all. The soul of this nation is being sacrificed to assuage the abject terror felt by too many white people in knowing that people of color will outnumber them in about 20 years.

One often hears it said that those white folks vote against their own interests, siding with tax cuts for billionaires over their own pocketbooks, refusing better healthcare because that means black people will get it, too. But Wilkerson says this misses the point. Those people are voting for their interests: It’s just that they have no interest higher than protecting whiteness — defending their caste.

Consider the 2016 election. “They were willing to lose health insurance now, risk White House instability and government shutdown, external threats from faraway lands, in order to preserve what their actions say they value most — the benefits they had grown accustomed to as members of the historically ruling class in America.”

It’s a truth that lends pungent urgency to Taylor Branch’s question. How many people would choose whiteness over democracy?

November is coming. So we’re about to find out.

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Leonard Pitts Jr. is a columnist for the Miami Herald.