America is a much less racist nation than it used to be, and I’m not just talking about the still remarkable fact that an African-American occupies the White House. The raw institutional racism that prevailed before the civil rights movement ended Jim Crow is gone, although subtler discrimination persists. Individual attitudes have changed, too, dramatically in some cases. For example, as recently as the 1980s half of Americans opposed interracial marriage, a position now held by only a tiny minority.

Yet racial hatred is still a potent force in our society, as we’ve just been reminded to our horror. And I’m sorry to say this, but the racial divide is still a defining feature of our political economy, the reason America is unique among advanced nations in its harsh treatment of the less fortunate and its willingness to tolerate unnecessary suffering among its citizens.

Of course, saying this brings angry denials from many conservatives, so let me try to be cool and careful here, and cite some of the overwhelming evidence for the continuing centrality of race in our national politics.

My own understanding of the role of race in U.S. exceptionalism was largely shaped by two academic papers.

The first, by the political scientist Larry Bartels, analyzed the move of the white working class away from Democrats, a move made famous in Thomas Frank’s “What’s the Matter With Kansas?” Mr. Frank argued that working-class whites were being induced to vote against their own interests by the right’s exploitation of cultural issues. But Mr. Bartels showed that the working-class turn against Democrats wasn’t a national phenomenon — it was entirely restricted to the South, where whites turned overwhelmingly Republican after the passage of the Civil Rights Act and Richard Nixon’s adoption of the so-called Southern strategy. ...