The Horserace Blog has a very clear explanation of the black vote and the Democratic Party. Also note the very clear and broader explanation of how and why the Democratic Party is without a base. He maintains, and I agree (although the point can be refined) that Kerry will lose the election for lack of black and Catholic support. It will not stretch your imagination to see what a bind the Demos are in after they lose this election: they stand for nothing (compared to their past) and have a base only in those states (California, Illinois, e.g.), where the GOP is incompetent or corrupt. I don’t know this guy, but he is good. Read it. 
I blogged about this a while back: "Let’s see now. The Catholic vote went for Gore in 2000 (Kyrie eleison) and Catholics polled for Kerry a few months ago. But Catholics now poll for Bush. And the Gender Gap is narrowing, if not quite disappearing. (And don’t forget the ’battleground’ states that are already being abandoned by the Kerry campaign as losses, nor the ’blue’ states that are being hotly contested by the Bush campaign.) So, tell me, somebody: how can the race be so close? What group(s) have shifted seismically towards Kerry to offset the shift towards Bush in two very large voting blocs?" That was before it came out that Bush has probably doubled his support among black voters.