This second map is based on census data and shows what the largest (self-reported) ancestry is in county of the United States. Take a look at it and you'll see that the interior south, where Obama could get no traction and almost the only part of the country where people voted more Republican in 2008 is the part of the country dominated by people who describe their ancestry as not German or English or Spanish or Irish but "American."via Ben Smith and Ben Smith
This sounds at first blush like simple ignorance of the concept of ancestry, but the map's annotation notes that "The region had very low levels of immigration for 200 years. ... According to the 1870 census, less than 2% of the south was immigrants." In most of the rest of the deep south's counties the biggest ethnic group is African-Americans descended from slaves. While the rest of the country has gotten more ethnically mixed recently, the south, and I'd guess particularly Appalachia, has had a nearly static, isolated population for two centuries.
And now those "American" Americans are the most reliable Republican voters.