Even as the economy slowly gathers steam, men like Mr. Campbell, who lack college degrees, are increasingly falling behind. Many manufacturing jobs that kept blue-collar workers afloat have vanished. And wages have plunged.

Between 1979 and 2007, wages for men under 30 with only a high school diploma fell nearly 29 percent, according to a 2011 study by Andrew Sum, a professor of economics at Northeastern University in Boston. And that was before the Great Recession and the weak economic recovery that has followed.