If you're a white American, you're more likely than not to vote Republican, though it's a close call. If you're white and male, or white and religious, or white and from the South, or white and old enough to collect Social Security, your odds of a GOP affiliation go up a good deal. If you happen to be a 70-year-old white evangelical gentleman from Tennessee, you're either Republican or exceedingly odd. About as odd as a black Republican. Ben Carson, a black retired neurosurgeon running for the Republican presidential nomination, is odd—and valuable. Black Republicans aren't quite unicorns, but they are capable of working a rare magic. Unlike the president, Mr Carson, a staunch Tea Party conservative, is a black man white Republicans will pay attention to when he talks about race. After a young white supremacist murdered nine black people in a Charleston church, another Republican doctor, Rand Paul, a Kentucky senator and presidential contender, said that "There's a sickness in our country. There's something terribly wrong." The problem, he reckoned, is rooted in "people not understanding where salvation comes from". Other Republican candidates for the top job similarly avoided mention of race. Mr Carson's diagnosis immediately stood apart. Dylann Storm Roof was led to kill not by some vague spiritual malaise, he explained, but by virulent racism. "Let's call this sickness what it is," Mr Carson said, "so we can get on with the healing".

Taking a swipe at his Republican rivals, Mr Carson went on to say that "there are people who are claiming that they can lead this country who dare not call this tragedy an act of racism, a hate crime, for fear of offending a particular segment of the electorate." Mr Carson warned that the refusal to acknowledge and condemn racism when it rears its ugly head allows "the spiritual sickness" of racism to fester and grow. He said, "If we teach [our youth] it is okay to deny racism exists, even when it's plainly staring them in the face, then we will perpetuate this sickness into the next generation, and the next.”

Archive: Why some Republicans think a charismatic brain surgeon can win the White House This is a message Republicans need to hear. When Democrats try to send it, Republicans tune out. They feel attacked, unjustly accused and condescended to. The same message from a black Republican produces less resistance. It is politically incorrect, and therefore courageous and admirable, simply to be a black Republican. That Mr Carson is a black Republican running for president is proof of his intellectual independence and immunity to racial groupthink. Therefore, if Mr Carson, who is willing to see everything else the way white Tea Partiers do—who seems to be currying favour with white Republicans in every other way--has something uncomfortable to say about race, it is automatically credible. It cannot possibly be "race hustling" liberal cant. There must be something to it. So the message is, finally, heard. Eventually, it may even be taken to heart. This dynamic explains why black Republicans are among the most progressive forces in American politics. Perhaps the main impediment to progress in the struggle for racial equality in America is the obliviousness of whites to the persistence of racism. The privilege of whiteness enables the view that skin colour has no bearing on one's chances in life. Systemic racial bias tends to be invisible to those who only enjoy the upside. If you don't experience the daily, demoralising frictions of endemic racism, and you aren't friends with anyone who does, it's very easy to imagine there's no problem. The real, practical difference between white Republicans and white Democrats is that almost 90% of America's blacks are Democrats, and white Democrats need them, and need to listen to them, in order to get and keep power. Accordingly, white Democrats are more likely than white Republicans to believe that race still matters, that racism is a real problem, and that it is at best premature to aspire to a policy of official colorblindness, because America remains far from colorblind. White Democrats might not have many, or any, black friends. But they do have trusted black political allies who tell them the truth about race, and that matters. White Republicans are unlikely to have either, and that matters, too. Stephen Colbert's "I don't see colour" joke is a joke on Republicans, rather than white Americans generally, in no small part because of the overwhelming identification of black Americans with the Democratic Party. When white Republicans are confronted with the invisible-to-them realities of race in America, the articulation of that reality tends to comes across with a hostile partisan cast. After all, pretty much everyone in a position to speak about racism with any real specificity and personal force is a Democrat. That's why it matters enormously when Mr Carson scolds fellow Republicans for refusing to acknowledge that racism is a real cultural pathology, or when he goes on CNN and tells the story of how, after his family moved into a new house in rural Maryland, a neighbour displayed a Confederate battle flag on his barn, "as a message to us". Mr Carson certainly knew what it meant, and so did his other, more welcoming neighbours, who raised American flags in response. This, Mr Carson says, "shamed" the racist among them to take down his flag. "We are social beings," Mr Carson noted, explaining the importance of the symbolism of flags. "Let's send the right messages to each other and I think that will take care of a lot of our problems".

The trouble is that if white Republicans are actually going to receive "the right message" about race, and the confederate battle flag, more black Republicans are needed to send them. And here we run into a sort of paradox. Because maintaining a lock on the black vote is so vital to the Democrat's electoral prospects, Democratic partisans, white and black, tend to cast black Republicans as unacceptable defectors from the true cause of social justice, who function mainly to gratify and comfort white Republicans by assuring them they aren't as racist as the Democrats say. And it's a little bit true. Black Republicans do serve to ease the white Republican conscience. But then that's what leaves many white Republicans, who would otherwise shut it out, attentive for once to truths about the black American experience. It would be an awful irony if the intransigent obliviousness of white Republicans, which stands hugely in the way of further progress toward racial equality, were actively, if unintentionally, reinforced by Democrats policing the race line.