Paul Rosenberg has diaried here that wealthier Southern white flight to the Republican Party has been a significant driver of today's political alignments. The same theme has recently been explored by Paul Krugman at his blog. Krugman calls attention to an excellent academic article on the myth of the rich Democrat by Larry Bartells at Princeton. These things seem to run in fours. Paul Gelman at my favorite statistics website Statistical Modeling and Causal Inference has similar research on class, race, voting and between the states.
The conclusions from all four, add up to a powerfully convincing explanation. As Krugman puts it "once you take the great southern switch into account, there isn't much left to explain.... White men didn't turn against the Democrats; Southern white men turned against the Democrats. End of story." Class separation on voting has increased from 4% in the 1952-1972 period to 14% in the 1976-2004 period. RICH white southerners became Republican, while POOR white Southerners remain Democrat. Class voting differences are more dramatic in poor states than in rich states.
The piece de resistance is a wonderful graphic from Andrew Gelman that collapses this issue into three powerfully explanatory images worth a 1000 words Some cool graphs of rich states and poor states showing famous red-blue maps for Bush vs Kerry disaggregated into three income levels, poor, middle and rich (rich is above the 95th percentile, poor is up to the 37 percentile). Here are Gelman's images: