This is an interesting lesson in how the South has changed. Remember, this is just a comparison between Clinton and Obama. I am pretty much leaving 2000 and 2004 out of the picture, with only passing references.
Map 1: The common electoral column won by both Clinton and Obama both times
These 23 states and DC were won by both Clinton and Obama in both of their respective elections. Take away Ohio and New Hampshire and you have Al Gore's complete electoral column from 2000. Then take away Iowa and New Mexico but return New Hampshire and you have John Kerry's complete electoral column from 2004.
There are two states that Clinton won only once, but not twice, that Obama never won: MT and AZ.
There are two states that Obama won only once, but not twice, that Clinton never won: IN and NC.
There are 6 southern states that Clinton won twice, that Obama never won. I call these states the Clinton 6.
Map 2: The "Clinton 6"
These states are within two regions: the Appalachian Region, which is a fixed geographical region, and the so-called "Bible-Belt", which is an estimated area of where the fundamental Christian movement is strongest.
It is probably more helpful to see the general margins with which Clinton won these six states.
Map 3: The "Clinton 6", shaded according to margin averages
Kentucky was the leanest of the Clinton 6, having gone for Clinton by +3.21% and +0.96% in 1992 and 1996, respectively. Since 2000, Kentucky has gone solidly for the GOP by no less than +15.13% and gave Mitt Romney the highest margin in the Bluegrass state since 1972.
Tennessee was the next leanest of the Clinton six, having gone for Clinton by +4.65% and +2.41% in 1992 and 1996, respectively. Though it switched narrowly to Bush 43 in 2000, since 2004, Tennessee has gone solidly for the GOP by no less than +14.27% and gave Mitt Romney the highest margin in the Volunteer state since 1972, as was the case in Kentucky.
Louisiana was the third leanest margin of the Clinton six, having gone for Clinton by +4.61% and +12.07% in 1992 and 1996, respectively. Notice that Louisiana and Tennessee went for Clinton by almost identical margins in 1992 but then diverged strongly from each other in 1996, where LA swung by a landslide more to the Democratic party, while TN and KY both swung more to the Republican party. But, like Tennessee, though it switched narrowly to Bush 43 in 2000, since 2004, Louisiana has gone solidly for the GOP by no less than +14.51% and gave Mitt Romney the highest margin in the Pelican State since 1984, Ronald Reagan's historic re-election.
Missouri's electoral direction is similar to Kentucky and Tennessee, but it went for Clinton by much more solid margins, by +10.15% and +6.30% in 1992 and 1996, respectively. But the similarities for Missouri end there. Since 2000, it has been a GOP single digit state, albeit a (currently) +9.62% margin for Romney and also the largest GOP win here since 1984.
West Virginia and Arkansas were the two strongest of the Clinton 6 and both were landslide wins both times around, albeit with swings in different directions. Wow, what a difference 20 years makes.
Clinton won West Virginia by +13.02% and +14.75% in 1992 and 1996, respectively, so the state swung more to the Democratic Party in 1996. But from 2000 on, it has gone for the GOP by ever increasing margins, from +6.32% for Bush 43 in 2000 to (currently) +26.86% for Mitt Romney, a more than 20 point swing to the Republican Party since 2000 and a 33 point swing since 1992. Consider that: in 20 years, 1/3 of the West Virginian electorate has decisively switched sides. This is important to remember when you see the map of Appalachia, coming up soon.
Clinton won his home state of Arkansas by the largest margins both times: by +17.72% and +16.94% in 1992 and 1996, respectively, but the state swung slightly Republican in 1996 and has never looked back since then. Since 2000, Arkansas, just like West Virginia, has gone for the GOP by ever increasing margins, from +5.44% for Bush 43 in 2000 to (currently) +23.68% for Mitt Romney, an 18 point swing to the Republican Party since 2000 and a 35 point swing since 1992. So, similarly to West Virginia, slightly more than 1/3 of the Arkansan electorate has decisively switched sides and both states gave Romney the largest GOP win since Nixon in 1972. It is also possible that, when the final canvasses come in, the Romney may even surpass Nixon's 1972 statistic in West Virginia. Wait and see.
So, that was a detailed description of the Clinton 6.
Now, let's find out where Appalachia is, exactly:
Map 4: Appalachia
We can see that West Virginia, one of the Clinton 6, is the only state to be entirely within Appalachia and it is the state of these six which gave Romney his largest "Appalachian" margin of 2012. Notice that Appalachia also goes through a huge swatch of Pennsylvania, Ohio, Alabama, and to a lesser degree, Virginia, North Carolina and Mississippi.
And an interesting detail: here is an economic map of Appalachia. The legend is self-explanatory:
Map 5: economic map of Appalachia
Notice that West Virginia and Kentucky, which gave Romney some of his highest margins in 2012, were among the most economically distressed states in Appalachia and in the Union.
But there is another region to take into account: the "Bible Belt".
Map 6: the Bible Belt
This is fairly confirmed by a polling study of religiousity that Gallup did in 2001 (note: since it's terrible polling record from the 2010 mid-terms and the 2012 GE, I am including this map with a grain of salt):
Map 7: Gallup's map of religiousity in the USA
We can see that all of the Clinton 6 are within both areas..
With that in mind, let's see how the Republican states adjacent to the Clinton 6 did in 1992 and 1996:
Map 8: The Clinton 6 with adjacent GOP states, colored by margin level
We can see that the adjacent bible belt states were all lean or very lean GOP wins in 1992 and 1996. The exact stats for those states are here: Oklahoma, Texas, Mississippi, Alabama, Georgia, South Carolina, North Carolina and Virginia.
And then there is the "Obama 3"
There are two states that Obama won twice, which Clinton won only once: FL, CO
And there is one state that Obama won twice, which Clinton never won: VA
Not only that, in all three cases, these were majority wins for Obama both times, in 2008 and in 2012.
If we add the Obama 3 to the Clinton 6 map, then it looks like this.
Map 9: The Clinton 6 and the Obama 3, 1992-1996
This is the behaviour of the Obama 3 and Clinton 6 in 1992 and 1996.
Now, these same nine states in 2008-2012.
Map 9: The Clinton 6 and the Obama 3, 2008-2012
Absolutely amazing how the maps, even in terms of color intensity, are pretty much mirror-images of each other. Here, in an animated .gif, you can see the change quite vividly:
Map 10: Clinton 6 and Obama 3, shift from 1992-1996 to 2008-2012
FACIT: some historical firsts.
Obama is the only Democratic President in history to lose WV, KY, TN, MO, AR and LA twice in a row, meaning that these once core-Democratics states were never a part of his electoral column. In fact, every other two-term Democratic President (Cleveland, Wilson, FDR, Clinton) has won these states two times except for Wilson in WV in 1916.
Obama is the first Democratic President since FDR to win VA, CO and FL twice in a row.
So, not only has there been electoral shift within the Union, there has been verifiable electoral shift within the standard Democratic electoral column.