Obama and Romney each have a plan to lift Middle America from its rut, but election-year promises aren't going to fix an issue that's been brewing for decades.

"Both narratives are virtually irrelevant to the sorry situation of the middle class, which began long before the financial crisis and recession. Incomes in the broad middle have gone nowhere for more than 20 years after rising slowly but steadily through most of the 20th century. Why? Many theories have been advanced, but the one that holds up best is set out by Harvard economists Claudia Goldin and Lawrence Katz in articles and a book, The Race Between Education and Technology. The economy continually demands higher-level skills from workers, they argue, and for most of the 20th century the U.S. workforce kept up. In 1900 few people stayed in school past eighth grade; by 1970 a large majority finished high school, and many went on to college. American workers became the world's best-educated and earned the rewards.

Then, in the 1970s, America's level of education stopped rising. The high school graduation rate peaked at 77% in 1969 and has since dropped to about 69%; college rates, too, stopped rising. The economy kept demanding more workers with advanced skills, but we stopped producing more. At the same time, other countries relentlessly educated their people, so the U.S. workforce fell from No. 1 in the world to the middle of the pack. Result: The minority of workers with advancing skills became more valuable, while the broad middle got flat or even falling pay.

But infotech makes middle-class jobs disappear; software takes over routine back-office tasks, and infotech coordinates supply chains, so manufacturing jobs can be done by lower-paid workers abroad.

Nor is the problem that income inequality increased, because it didn't during the recession; top earners on average got clobbered even worse in the recession than the middle class did. The problem is that the middle class isn't supplying the new skills that the world is demanding. We can fix that problem."