The problem for southern Dems isn’t whites; many of them left long ago. It is the small but increasing number of blacks that have lost faith in the party.
Nationally, the problem for Dems is being viewed as the “non-white” party; there are simply not enough of them (yet) to win nationally. Hence, they have to try to keep “Kennedy-type” whites (usually females, or Chris Matthews) in the party, while trying to accomodate blacks and Hispanics (the whole time promising all of them affirmative action goodies, for which they are fighting each other).
In the unlikely event the Democrats begin hemorrhaging black support, we may see the end of the Democratic Party as a political force in this country. That day isn’t here yet.