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.

And this party-switching, in turn, was what drove the rightward swing of American politics after 1980. Race made Reaganism possible. And to this day Southern whites overwhelmingly vote Republican, to the tune of 85 or even 90 percent in the deep South.

The second paper, by the economists Alberto Alesina, Edward Glaeser, and Bruce Sacerdote, was titled “Why Doesn’t the United States Have a European-style Welfare State?” Its authors — who are not, by the way, especially liberal — explored a number of hypotheses, but eventually concluded that race is central, because in America programs that help the needy are all too often seen as programs that help Those People: “Within the United States, race is the single most important predictor of support for welfare. America’s troubled race relations are clearly a major reason for the absence of an American welfare state.”

Now, that paper was published in 2001, and you might wonder if things have changed since then. Unfortunately, the answer is that they haven’t, as you can see by looking at how states are implementing — or refusing to implement — Obamacare.

For those who haven’t been following this issue, in 2012 the Supreme Court gave individual states the option, if they so chose, of blocking the Affordable Care Act’s expansion of Medicaid, a key part of the plan to provide health insurance to lower-income Americans. But why would any state choose to exercise that option? After all, states were being offered a federally-funded program that would provide major benefits to millions of their citizens, pour billions into their economies, and help support their health-care providers. Who would turn down such an offer?

The answer is, 22 states at this point, although some may eventually change their minds. And what do these states have in common? Mainly, a history of slaveholding: Only one former member of the Confederacy has expanded Medicaid, and while a few Northern states are also part of the movement, more than 80 percent of the population in Medicaid-refusing America lives in states that practiced slavery before the Civil War.

And it’s not just health reform: a history of slavery is a strong predictor of everything from gun control (or rather its absence), to low minimum wages and hostility to unions, to tax policy.

So will it always be thus? Is America doomed to live forever politically in the shadow of slavery?

I’d like to think not. For one thing, our country is growing more ethnically diverse, and the old black-white polarity is slowly becoming outdated. For another, as I said, we really have become much less racist, and in general a much more tolerant society on many fronts. Over time, we should expect to see the influence of dog-whistle politics decline.

But that hasn’t happened yet. Every once in a while you hear a chorus of voices declaring that race is no longer a problem in America. That’s wishful thinking; we are still haunted by our nation’s original sin.