Romney's challenge in white-collar America underscores how thoroughly a "class inversion" has reshaped the electoral landscape. From the Depression into the 1970s, Republicans were the party of white-collar whites and Democrats the party of whites who worked with their hands. Every Democratic nominee from Adlai Stevenson through Jimmy Carter ran substantially better among noncollege than college-educated whites. But in his two victories, Bill Clinton did as well among college-educated as noncollege whites. In 2000, Al Gore ran four points better among those well-educated whites; the gap widened to six points for John Kerry in 2004 and to seven for Obama. This year, a gaping class inversion runs through not only national measures like the NBC/WSJ poll but all of the recent Quinnipiac CBS/New York Times swing-state polls.

Other measures find the same trend. As the Cook Political Report's David Wasserman and I have calculated, Ronald Reagan in 1984 won 82 of the 100 counties with the highest proportion of college graduates. But Democrats have taken at least half of those counties in every election since 1992; Obama captured 78 of them, receiving a resounding 62 percent of their combined votes.

Likewise, Atlantic Senior Editor Richard Florida and his colleagues at the University of Toronto's Martin Prosperity Institute have used Bureau of Labor Statistics to estimate the share of every county's workforce that belongs to what he has labeled "the creative class." Those are workers -- from architects to corporate managers -- who Florida defines as being "paid to use their minds." The 100 counties with today's highest share of creative-class workers split evenly between the two parties in 1988, Wasserman calculated; but in each election since, the Democrats have won about three-fifths of the combined vote from those counties, with Obama establishing a new high at 64 percent. Meanwhile, Obama drew less than two-fifths of voters in both the 100 counties with the fewest college-graduates and the fewest creative-class workers.

Social issues explain much of this reversal: White-collar whites, especially women, tend to take more liberal positions on questions like abortion than their blue-collar counterparts (or most minorities, for that matter). And while college-educated men often respond to conservative tax-and-spending arguments, the women show more openness to activist government.

In a race this close, the margin in every group matters. Romney's path would be eased if he trimmed, even slightly, Obama's 4-1 advantage among minorities in 2008. Conversely, Obama's ad barrage portraying Romney as an uncaring plutocrat is aimed largely at suppressing the president's losses among blue-collar whites, especially women. And yet to win re-election, he almost certainly needs to run closer to his 2008 number among college than non-college whites, as most polls now show him doing.