“A big reason why we still have overly high unemployment is that we have a demand challenge,” she added. “Wealthy people are doing really well, and we’re still not getting high growth rates.”

Middle-out economics is rooted in liberals’ thinking dating back to the first Clinton campaign in 1992 at least. Mr. Obama himself put forward many of its ideas in a 2005 speech at Knox College in Illinois and in his book “The Audacity of Hope.”

“Middle-out economics is not only an affirmative description of a set of ideas of where growth comes from in the economy, but an inherent criticism of conservative views of where growth comes from in the economy,” Ms. Tanden said. But White House officials and many on the left said that two factors had recently crystallized the idea: rising inequality and the 2012 presidential campaign.

Since the late 1970s, the top 1 percent of earners has gained an increasingly large share of overall income. The recession interrupted that trend, but the rich have rebounded during the sluggish recovery while other Americans have struggled. The incomes of the 1 percent grew more than 11 percent between 2009 and 2011, but the incomes of the 99 percent actually shrank.

Even before the recession, middle-class families were struggling. Rapidly growing health costs ate away at paychecks, and technological change and economic globalization hit blue- and white-collar workers alike. The median household income, adjusted for inflation, has fallen about 9 percent since its peak in 1999, though the economy has expanded by about 23 percent.

Politicians left, right and center agree that the middle class is being squeezed. But the policies they have proposed to alleviate those pressures are sharply different — and the conservatives’ ideas have galvanized liberals.

Politicians — including Representative Paul D. Ryan, Republican of Wisconsin, the influential chairman of the House Budget Committee and Mr. Romney’s running mate — have argued that Washington needs to balance the budget, slash taxes, reduce regulations and get out of the way of American businesses and markets to benefit consumers and return the country to prosperity.