Jonathan Capehart is a Post opinion writer.

With the Democratic primary in South Carolina upon us, the question isn’t whether the presumed firewall of African American voters for Hillary Clinton will hold. I firmly believe that it will. The question is why. Yes, a lot of it has to do with fealty to President Obama. But it also has to do with what Clinton is saying to African Americans and how she says it.

“Any discussion of the Democratic base must include the acknowledgment that that base is heavily Black,” explains Steve Phillips in his insightful new book “Brown is the New White.” Phillips argues that a “New American Majority” has formed within the voting-age population in the United States: “Progressive people of color now comprise 23 percent of all the eligible voters in America, and progressive Whites account for 28 percent of all eligible voters,” he writes. “The New American Majority electoral equation requires securing the support of 81 percent of people of color and 39 percent of Whites.”

This demographic reality brings the Democratic campaigns for president into clearer focus. Income inequality and Wall Street excess animate both halves of that “New American Majority,” so it’s no surprise that both Clinton and her rival, Vermont Sen. Bernie Sanders (I), talk a lot about them. Same goes for criminal justice reform and immigration. But not every issue is of equal importance to people of color and progressive whites, and this is the key to Clinton’s advantage. There are three reasons Clinton’s firewall of black voters won’t #feelthebern in South Carolina and beyond.

First, Obama. His approval rating among African Americans is 89 percent in the latest Gallup tracking poll. This explains why Clinton has left no daylight between herself and the man who bested her in 2008 and for whom she worked as secretary of state. And it explains why she highlights the many times that Sanders argued for a primary challenge to Obama in 2012.

Second, Clinton doesn’t shy away from race. Sanders talks about race, too, of course. But he seems to do so at a remove, and his attempts to make a convincing link between his economic message and race continue to fall short.

“We have to begin by facing up to the reality of systemic racism, because these are not only problems of economic inequality,” Clinton said at Harlem’s Schomburg Center for Research in Black Culture last week. “These are problems of racial inequality. And we have got to say that loudly and clearly.” And Clinton’s pitch to black voters is part and parcel of her larger pitch to all voters. She was asked to “look beyond diversity to wealth creation” during an interview with BET recently. “The fastest-growing group of small-business owners are black women,” she said. “We need to do more to help them get access to the credit that they need.”

The third reason is perhaps the most important, because of how deeply it resonates with African Americans: Clinton openly talks about the necessary role that whites must play in healing and bridging the racial divide.

“Ending systemic racism requires contributions from all of us, especially those of us who haven’t experienced it ourselves,” she said in Harlem. “White Americans need to do a better job of listening when African Americans talk about the seen and unseen barriers that you face every day. We need to recognize our privilege and practice humility, rather than assume that our experiences are everyone’s experiences.”

To BET, she said: “I’m trying to lead a conversation that doesn’t just address African Americans, but also goes right at talking with white Americans about the perspective they need to have in hearing about the barriers that African Americans face, not only in the criminal justice system, not only in the rates of incarceration, as devastating as those are, but in employment, in education, in housing.” This is similar to what she said at the CNN town hall on Tuesday.

Do not underestimate how refreshing this is to African American ears. For generations, blacks have chafed at the notion that unpacking our nation’s racial baggage is a chore solely for them. That the lingering effects of slavery and Jim Crow are only their burdens to bear. That today’s whites are absolved from responsibility for helping to address the continuing consequences of yesterday’s offenses. For a potential president of the United States to acknowledge this and to do so from a knowing place — to demonstrate that she’s thought deeply about it and gets it — will elicit a ready chorus of “amen.”

For months, Sanders and his supporters have said that black voters will grow to like him once they get to know him. But the Democratic caucuses in Nevada last Saturday were a sign that the true base of the Democratic Party isn’t being moved by his message. By getting the substance right, Clinton has set the bar too high with African American voters for Sanders to clear it.