If Obama survives, the shifting composition of the electorate will also be a—and perhaps the—critical factor. In 1984, whites without a college degree represented 61 percent of all voters, and college-educated whites just 27 percent. But by 2008, noncollege whites had plummeted to just 39 percent of all voters, and college-educated whites increased to 35 percent. Noncollege white men, consistently the GOP’s best group, fell from 28 percent of all voters in 1984 to just 18 percent in 2008; the waitress moms also slipped from 33 percent to 21 percent over that period. White men with a college degree, who traditionally lean Republican but did so by smaller margins in the past two elections, essentially maintained their share of the electorate over those years, increasing from 16 percent to 18 percent.

But the biggest gains have been recorded among two groups that favor Democrats. With women now earning about three-fifths of college degrees, college-educated white women have increased their share of the vote from 11 percent in 1984 to 17 percent in 2008. (These upscale, Democratic-leaning women could conceivably cast more votes than blue-collar men this year.) Minorities have grown even faster, rising from 12 percent of the electorate in 1984 to 23 percent in 2004 and 26 percent in 2008. Recent analyses of census data show that minorities make up 29 percent of 2012’s eligible voters (although it’s unclear whether that population growth will produce comparable gains in the electorate.) And with that burgeoning population, Republicans now see very few openings.