Blank map apparently applicable to 2012:
In 1976, Jimmy Carter won all former-Confederate states except Virginia. Color those states green -- aqua if Carter, Clinton (at least once), and Obama won the state [Florida], light green if Carter and Obama (but not Clinton) won it [North Carolina] , medium if Clinton won it but Obama lost it by 10% or larger margins (AR, LA, TN) -- and add Kentucky (which had a secessionist government in one part of the state for a time) and West Virginia even if it isn't particularly "southern" because it follows the pattern. Color Georgia and Missouri (southern Missouri really is Southern) -- Carter won these states, Clinton won them both at least once, and Obama wasn't far from winning them both.
Carter is the last Democrat to have ever carried Texas, Mississippi, Alabama, or South Carolina. Color those pine-green. Now color Virginia yellow -- neither Carter nor Clinton ever carried the state, but Obama did. Dubya won ever one of these states.
Now color in deep blue all of the states that President Obama has no reasonable chance of winning outside of the South in 2012. That includes only three of five electoral votes of Nebraska, but you get the idea:
Add the Dakotas, NE-01, and Arizona as "unlikely", Indiana and NE-02 as freakish circumstances in 2008, and Montana because its three electoral votes are unlikely to make a difference, in medium blue, and you get
With all Southern and near-Southern states blocked off from the Democratic nominee, the Democratic nominee of 2012 must win the entire block of states that neither Gore lost in 2000 nor Kerry lost in 2004 (deep red), states that one or the other lost once (IA, NH, NM -- medium blue) and either Ohio or a combination of Nevada and Colorado.
Kerry would have won in 2004 had he also won Iowa and New Mexico and picked off Ohio or Colorado; in 2008, Barack Obama could have done so too -- while winning nothing even arguably Southern. There's just not much wiggle room
(Obama was not going to win Indiana without winning Ohio as well, and in 2012 he will not be able to win Arizona without winning both Colorado and Nevada).