Lots of it here. In particular, I think the Democrats relied too much on their polling, and the polling failed them. But I'll admit, I don't know what happened.

At this point, I recommend reading this symposium in Boston Review about the future of the Democratic party. It's long, but worth it, with ideas from a lot of smart professors, pundits, and other political types. Bush and friends are going to do a lot of damage over the next four years, and the only way to reverse those losses is to build a viable long-term movement. Progressives have done it before; they can do it again. 2006 is only a few years away.