The Democratic Parties continuing obsession with white southerners

From Andrew Jackson to James K Polk to Bill Clinton to John Edwards, the Democratic Party just can't seem to get over it's obsession with popular southern politicians.
Maybe it is because the democratic party originated from -- and up until the 60's was largely constrained too -- the south. Or maybe being from the south or at least somehow affiliated with anything southern, eliminates any sort of "elitist" label that can be thrown at them by political opponents.
Now statitstics don't lie, democrats have won 5 of the last 14 Presidential elections and Americans have only seen one incumbent Democratic president in 60 years, and this may go to show, that except on the local level (Democrats have in recent historical memory generally have held slim majorities in Congress) there's something about a national Democrat that the average American finds suspicious or just downright untrustworthy. Is it that they're just easy targets for a well oiled and ruthless Republican attack machine? Or is it that their nominating process continually spews forth weak candidates? Despite being a country that conventional wisdom has dubbed "center-right," roughly 38% of the country describes themselves as "Democrat" and another 15 % describe themselves as "left leaning independent." now simple math tells you right there that just a little bit more than the majority of the country describes themselves in one way or another as personally more affiliated with the party of the left. Now there's plenty of ways those numbers can be sliced and diced, but simply put, Democrats just can't seal the deal.
With the exception of the Johnson landslide in 1964, which started the "liberal wave" that lead to -- and was immediately fizzled out by: medicare, civil rights legislation and social security, the American consciousness has only allowed itself to vote for a democrat only when the Republican brand has completely failed (Carter) or a third party siphons 19% of the popular vote (Clinton.)
All 3 of the Democratic Presidents that have held office since Kennedy have been from the south, and Kennedy himself, being from the liberal bastion of Massachussetts, chose Johnson as a way to ensure that he could "lock up the south."Fellow Massachussetts men Michael Dukakis and John Kerry, perhaps following in Mr. Kennedy's footsteps, each also chose popular southern politicians as their running mates, Senator Lloyd Bentson from Texas and Senator John Edwards from North Carolina respectively. Dukakis himself has admitted that one of the only things he got "right" during his failed 1988 campaign was his choice in running mate. Kerry must've thought that Edwards' folksy southern charm and populist speaking style would perhaps offset that national suspicion America seems to have with mainstream democratic presidential candidates and perhaps help him demographically in places he himself as a candidate was struggling.
Let's look at the current race, Senator Barack Obama, the first major party candidate nominated from Illinois since Lincoln faces that same question and that same mainstream American suspicion. On the other hand, President Bush has driven his own parties brand into the ground, and this leaves fertile room for Mr. Obama, who has seen a laundry list of southern politicians listed as his potential running mates, the mostly prominent on that list being current Virginia governor Tim Kaine and former Georgia Senator Sam Nunn. If Obama breaks convention and chooses a running mate not from the south and wins, it would be the first time since 1940 that the nation chose a Democratic ticket not featuring at least one southern politician.
Also currently, it was just announced that former Virginia Governor Mark Warner will be giving the keynote address at this years Democratic National Convention. With John Edwards in disgrace over his extra-marital affair, the convention lacked a southern face, and who better to give it that face thenn the popular ex-governor and current senate candidate Mark Warner. If Warner follows what has seemed to be the typical path, he could be quite a formidable candidate for the presidency himself in maybe 4 - 8 years, Republicans would probably tremble at the idea of sending someone up agains yet another popular white democratic southern governor.
So what is the Democratic Party's obsession with all things Southern? Is it their desperate need to gain acceptance amongst the beer-swilling Nascar crowd? Their secret love of pork products? Or is it that they feel they are so out of step with mainstream America that they have to put that southern face on everything in a final plea to the American public that they really are the party of the common man.
Personally I don't think any amount of analysis can offer a solution, but until then, it's fun to think about.