Here's a county level map of presidential voting in 2004:
Here's a similar map for this election:
Not that much changed, though Obama made incremental progress in many places. Here, however, is where McCain did better than Republicans in 2004. Arizona and Alaska make sense, and of course southern Lousiana lost a lot of black Democrats. But McCain made his pickups almost exclusively in a particular geography--the upland south.
This is a rough breakdown of that region. It's a pretty distinctive part of the South. Slavery was never big here; there is virtually a total complement between this and the following graph.
The share of African-Americans.
Similarly, this is also where Bill Clinton won his votes in the Democrat primary (purple is where he won > 65% of the vote). Hillary Clinton did very well here in those areas as well.
This gets at ethnic breakdown in this area. This is be a bit hard to read, but basically the plurality ethnic group reported to the census here is "American"--these people are Scotch-Irish who predominately identify by nationality. The regions where such groups are numerous map very strongly to those places where McCain/Palin grew the Republican vote share. Household incomes tend to be fairly low, with some of the biggest pockets of isolated poverty anywhere in the country.
Presumably this reflects the impact of adding Palin to the ticket. You have cultural identification by "real Americans," a strong evangelical turnout, and racism, though I suspect Condoleezza Rice or Colin Powell would do well here. Further South, record turnout of black voters pushed Obama's share upwards, while further North, social conservatism, broadly, is a smaller force.
This illustrates the point that the South is both "larger" and "smaller" than people think. The Deep South plantation economy was restricted to the far southern geographies where that was economically viable, while broader southern culture is shared by a larger community of Scotch-Irish that stretches into Ohio and Pennsylvania.
Politically, it doesn't seem to make a lot of sense in retrospect for Republicans to double down on this demographic. One of the post-election quotes from MN governor Pawlenty caught my attention. The original Sam's Club Republican was caught saying that his party needs to focus on attracting women, Hispanics, blacks, and young people. Well. What demographics was your party targeting to begin with?
The young vote doesn't bode well for them, as young people these days are fairly liberal on a range of economic and social issues. Some of this will obviously fade away over time, but the social liberal bit will probably stay; roughly, every generation moves out a step more liberal than the previous one and stays there. The cost of catering to the real Americans is felt in the plummeting support Republicans see among young voters, minority voters, and the educated. Obviously, these groups are pretty large and growing, while whole communities of Rockefeller Republicans are going extinct. The electoral benefits are pretty slim, as the bordering states were Republican anyway. The Republicans faced a very bad fundamental position and were probably going to lose barring some crisis. But McCain's decision to head even further right after winning the Republican nomination, target this crowd through a VP pick, and then run a campaign centered on inconsequential right-wing dogma points and attack ads did little to endear him to the broad swaths of American independents who swing randomly from party to party, and for whom McCain is actually fairly popular. It's enough to make you nostalgic for some Rovian tactics. At least he realized that you need more than half of the population to win, even if hubris over statistically dubious "political realignments" did them in.