Mr. Trump’s supporters are practiced at purposeful blindness. That his political life started with denying, without evidence, that Barack Obama is American — that this black man could truly be the legitimate president — is simply ignored. So, too, is his history of housing discrimination, his casual conflation of Muslims with terrorists, his reducing Mexican-Americans to murderers and rapists. All along, his allies have watched racial pornography, describing black America as pathological. Yet they deny that there is any malice whatsoever in his words and actions. And they dismiss any attempt to recognize the danger of his wide-ranging animus as political correctness.

But the deepest rift is with the apologists, the “good” Trump voters, the white people who understand that Mr. Trump says “unfortunate” things but support him because they like what he says on jobs and taxes. They bristle at the accusation that they supported racism, insisting they had to ignore Mr. Trump’s ugliness. Relying on everyday decency as a shield, they are befuddled at the chill that now separates them from black people in their offices and social circles. They protest: Have they ever said anything racist? Don’t they shovel the sidewalk of the new black neighbors? Surely, they say, politics — a single vote — does not mean we can’t be friends.