TAMPA, FLORIDA — One way to think about the U.S. election this year is as a contest between the impact of a sour economy (advantage Romney) and the power of America’s shifting demographics (advantage Obama).
Put simply, the groups that support President Barack Obama most strongly — blacks, Hispanics, young people, unmarried women — have been growing as a share of the electorate. Those who support Mitt Romney the most — white working men, in particular — have not...