At the time [of Obama's 2008 election], some commentators, including me, hailed the onset of an enduring Democratic majority. And the arguments in defense of this view did seem to be backed by persuasive evidence. Obama and the Democrats appeared to have captured the youngest generation of voters, whereas Republicans were relying disproportionately on an aging coalition. The electorate's growing ethnic diversity also seemed likely to help the Democrats going forward.
These advantages remain partially in place for Democrats today, but they are being severely undermined by two trends that have emerged in the past few elections—one surprising, the other less so. The less surprising trend is that Democrats have continued to hemorrhage support among white working-class voters—a group that generally works in blue-collar and lower-income service jobs and that is roughly identifiable in exit polls as those whites who have not graduated from a four-year college. These voters, and particularly those well above the poverty line, began to shift toward the GOP decades ago, but in recent years that shift has become progressively more pronounced.
The more surprising trend is that Republicans are gaining dramatically among a group that had tilted toward Democrats in 2006 and 2008: Call them middle-class Americans. These are voters who generally work in what economist Stephen Rose has called "the office economy." In exit polling, they can roughly be identified as those who have college—but not postgraduate—degrees and those whose household incomes are between $50,000 and $100,000. (Obviously, the overlap here is imperfect, but there is a broad congruence between these polling categories.)