If you live and work in the professional communities of Boston or Seattle or Washington, D.C., it is easy to forget that nationwide, even among people ages 25 to 34, college graduates make up only about 30 percent of the population. And it is easy to forget that a family income of $113,000 in 2009 would have put you in the 80th income percentile nationally. The true center of American society has always been its nonprofessionals—high-school graduates who didn’t go on to get a bachelor’s degree make up 58 percent of the adult population. And as manufacturing jobs and semiskilled office positions disappear, much of this vast, nonprofessional middle class is drifting downward.