That makes Mr. Romney and his party vulnerable, as he clearly knows. He said on Wednesday that issues of wealth distribution should be discussed only “in quiet rooms.” And he accused the president of using an “envy-oriented, attack-oriented” approach, “entirely inconsistent with the concept of one nation under God.”

Mr. Romney’s image of a country where workers have nothing but admiration for benevolent, job-creating capitalists (and no one is so impolite as to mention jobs destroyed) bears very little relationship to reality. But his suggestion that it is un-American to talk about rising populist resentment is self-serving and hypocritical. Republicans, in particular, have eagerly stoked such resentments against minorities and the poor.

That was the essence of the “Southern strategy” that Republicans, beginning with Richard Nixon, used to urge white voters to defect from a Democratic Party that supported civil rights. It continued for decades with attacks on busing, affirmative action, immigration and welfare, and was sounded most recently by Mr. Gingrich, with his attacks on Mr. Obama as “the food stamp president.”

Fanning resentment of the poor — and deflecting attention from the relentless Republican defense of the rich — is also central to the party’s current political strategy. That’s why so many Republican candidates and lawmakers keep talking so angrily about poor people not paying federal income taxes. That’s how the Tea Party got started in 2009, when Mr. Obama proposed lowering interest rates for homeowners who were behind on their mortgages and conservative activists saw an opportunity to pit the affluent against their struggling neighbors. And that’s why Mr. Romney constantly accuses the president of trying to create “an entitlement society,” which is simply a variant on Ronald Reagan’s welfare-queen anecdotes.

And yet if Democrats dare to point out that the income gains of the top 1 percent have dwarfed everyone else’s in the last few decades, they are accused of whipping up class envy. Alan Krueger, chairman of the White House Council of Economic Advisers, noted in a speech on Thursday that the median income in the United States had actually declined since 1999, shrinking the middle class while the income of the top 1 percent soared. Such inequality is corrosive. And pointing it out has nothing to do with envy and everything to do with pressing for policies to help America’s struggling middle class.