How Much Realignment Has There Been?

Susan G at Daily Kos quotes Larry Bartels on the question of how the Democratic Party coalition has changed since the New Deal:

[T]he net decline in support for Democratic presidential candidates among white voters over the past half-century is entirely attributable to partisan change in the South. It is equally notable, in light of the alleged abandonment of the Democratic Party by working-class cultural conservatives, that white voters in the bottom third of the income distribution have actually become more loyal in their support of Democratic presidential candidates over this period. Republican gains have come not among "poorer folks" but among middle- and upper-income voters--and even those gains have been concentrated entirely in the South.

I'm suspicious that the phrase "net decline" hides a multitude of sins, but it is still worth identifying the most important driving components of political change.