While white Southerners have been voting Republican for decades, the hugeness of the gap was new. Mr. Obama often lost more than 40 percent of Al Gore’s support among white voters south of the historically significant line of the Missouri Compromise. Two centuries later, Southern politics are deeply polarized along racial lines. It is no exaggeration to suggest that in these states the Democrats have become the party of African Americans and that the Republicans are the party of whites.
The collapse in Democratic support among white Southerners has been obscured by the rise of the Obama coalition. Higher black turnout allowed the Democrats to win nearly 44 percent of the vote in states like Mississippi, where 37 percent of voters were black. But the white shift is nearly as important to contemporary electoral politics as the Obama coalition. It represents an end, at least temporarily, to the South’s assimilation into the American political and cultural mainstream.