A specter haunts America: downward mobility. Every generation, we believe, should live better than its predecessor. By and large, Americans still embrace that promise. A Pew survey earlier this year found that 48 percent of respondents felt that their children's living standards would exceed their own. Although that's down from 61 percent in 2002, it's on a par with the mid-1990s. But these expectations could be dashed. For young Americans, the future could be dimmer.

Along with jobs, the 2012 presidential election could be fought over this issue. "Can the Middle Class Be Saved?" worried a recent cover story in The Atlantic. Pessimism rises with schooling. In the Pew poll, 54 percent of respondents with a high-school diploma or less felt their children would do better; only 35 percent of graduate school alums agreed. "A kind of depression has set in," writes Washington Post columnist Richard Cohen. "We've lost our mojo, our groove."

It can be argued that all this glumness repeats a historical error: projecting the present onto the future. Just because the economy is rotten today doesn't mean that it will always be. After World War II, the Nobel Prize-winning economist Robert Fogel has recalled, there was widespread "alarm about massive unemployment." Eleven million veterans and 9 million defense industry workers had to be re-employed. People feared a new depression. It didn't happen, because pent-up demand for homes, cars and appliances fueled a hiring boom.