We are told, for example, that conservatives are against big government and high spending. Yet even as Republican governors and state legislatures block the expansion of Medicaid, the G.O.P. angrily denounces modest cost-saving measures for Medicare. How can this contradiction be explained? Well, what do many Medicaid recipients look like — and I’m talking about the color of their skin, not the content of their character — and how does that compare with the typical Medicare beneficiary? Mystery solved.

Or we’re told that conservatives, the Tea Party in particular, oppose handouts because they believe in personal responsibility, in a society in which people must bear the consequences of their actions. Yet it’s hard to find angry Tea Party denunciations of huge Wall Street bailouts, of huge bonuses paid to executives who were saved from disaster by government backing and guarantees. Instead, all the movement’s passion, starting with Rick Santelli’s famous rant on CNBC, has been directed against any hint of financial relief for low-income borrowers. And what is it about these borrowers that makes them such targets of ire? You know the answer.

One odd consequence of our still-racialized politics is that conservatives are still, in effect, mobilizing against the bums on welfare even though both the bums and the welfare are long gone or never existed. Mr. Santelli’s fury was directed against mortgage relief that never actually happened. Right-wingers rage against tales of food stamp abuse that almost always turn out to be false or at least greatly exaggerated. And Mr. Ryan’s black-men-don’t-want-to-work theory of poverty is decades out of date.

In the 1970s it was still possible to claim in good faith that there was plenty of opportunity in America, and that poverty persisted only because of cultural breakdown among African-Americans. Back then, after all, blue-collar jobs still paid well, and unemployment was low. The reality was that opportunity was much more limited than affluent Americans imagined; as the sociologist William Julius Wilson has documented, the flight of industry from urban centers meant that minority workers literally couldn’t get to those good jobs, and the supposed cultural causes of poverty were actually effects of that lack of opportunity. Still, you could understand why many observers failed to see this.

But over the past 40 years good jobs for ordinary workers have disappeared, not just from inner cities but everywhere: adjusted for inflation, wages have fallen for 60 percent of working American men. And as economic opportunity has shriveled for half the population, many behaviors that used to be held up as demonstrations of black cultural breakdown — the breakdown of marriage, drug abuse, and so on — have spread among working-class whites too.