On economic policy, Barack Obama has left Mitt Romney an opening. The president has responded to a severe, continuing labor market slump with a four-year-old, marginally counterproductive tax increase proposal. His current economic agenda has little relevance to anything except his current political requirements: picking a political fight on tax-code equity to distract attention from his economic stewardship. It is the triumph of tactics and the surrender of seriousness.

In response, Romney put a single, characteristically hesitant toe through the opening. His NAACP speech Wednesday featured rich themes of promoting “equal opportunity,” building “human capital” and lifting people from poverty. But Romney’s supporting policies — on health care, energy, education reform — were resolutely untailored and uncreative.

“I am going to give the same message to the NAACP,” Romney said, “that I give across the country.” Apparently convinced that even a generic Republican can defeat President Obama, Romney seems intent on running as one.

To fill out an opportunity agenda, the Romney campaign might start by perusing a new report by the Economic Mobility Project of the Pew Charitable Trusts, which offers some challenging instruction across the political spectrum.

The Pew report analyzes how the incomes of families today compare to those of their parents’ generation. The good news: On every rung of the economic ladder, median income has gone up — not equally, but significantly. Even among the bottom 20 percent, income rose 74 percent between the two generations. Liberals need to accommodate the fact that the poor have not gotten poorer. The benefits of economic growth have been shared.

But relative mobility — the chance of rising to a higher income quintile — is stalled, particularly near the bottom. Even though many earn a bit more than their parents did, they aren’t moving up the income ladder. About 36 percent of families have actually fallen behind in relative terms, which drags America’s overall level of mobility to below that of many European countries.

Conservatives must take seriously that America’s poor are starting lower and rising less easily than in other developed nations — a problem often related to educational attainment and family structure. Income is not the only thing that matters. In the absence of mobility, inequality hardens into class division. The American ideal requires a realistic prospect of turning ability into achievement.

Witnessing a serious political discussion on the topic of mobility would require a plane ticket to London. Deputy Prime Minister Nick Clegg’s recent speech to the Sutton Trust indicted an economic system characterized by “entitlement at one end and exclusion at the other” and touted a series of interesting policies to close the educational attainment gap between rich and poor.

Labor Party leader Ed Miliband countered, in typical Labor fashion, that leveling equality is more important than opportunity. Along the way, Miliband delivered this trans-Atlantic taunt: “If you want the American Dream — go to Finland.”

Clegg bluntly raises the issue of social class, including his own — hanging a lantern on his privileged, Cambridge-educated background. “I know some people will say that I should keep quiet about social mobility,” he says. “That my birth, my education and my opportunities mean I have no right to speak up. I couldn’t disagree more. If people who’ve benefited from the system don’t speak up, we’ll never get anywhere. . . . I was lucky. But it shouldn’t be a question of luck.”

The topic of class comes more naturally to British than to American politicians. But the United States has a class problem, as does Romney. And Romney could help himself by addressing both.

As a governing matter, encouraging social mobility could eventually be a unifying, bipartisan goal. As a political matter, it would provide Romney a particular advantage. Obama’s message is now in full Labor Party mode: Soak the rich. But the smartest Republican response is not to defend the rich. It is to defend a fluid society in which everyone has the possibility of becoming richer. Economic redistribution is not the answer, but economic growth is not sufficient, either. Upward mobility requires the broad diffusion of skills and social capital.

Romney, while disarmingly recognizing his own advantages, should demonstrate some market-oriented innovation in extending advantages to others: promoting early-childhood education, high school completion, college attendance and graduation, parenting skills and wealth-building among the disadvantaged. It would be a powerful political message, addressing a serious need, in a manner consistent with conservative ideals.