The Democratic Prisoner Dilemma
This post by Markos goes a long way toward explaining the thinking behind Democrats who supported the bankruptcy bill (or at least voted for cloture). Atrios' comment on said post are also interesting (although I think he is incorrect to say that Markos' post is a "defense" of the Democrats).
Markos has it right that, on an individual basis, voting for the bankruptcy bill actually was a no-brainer for a lot of Democrats. There was very little political benefit to opposing it (consumers are not a standard Democratic constituency) and a serious threat if they voted against it (money from the financial sector drying up).
But Atrios has it right that the political benefit to the Democrats would have been enormous if they could have remained united on this. If they had then they would have had a great issue to hammer the Republicans next year ("Democrats: the party that looks out for you!"). But instead the bill has the veneer of bipartisanship support. Few Democrats can risk bringing it up as an issue because to do so would require them to attack their own party as much as the Republicans.
The problem is that Democrats have lost the sense of the commons. They no longer think in terms of what will benefit the party as a whole but instead think only of what will benefit them individually. As a result, the Republicans and their corporate paymasters have learned to play a classic case of The Prisoner's Dilemma against the Democrats. The choices for Democrats are stark: they can stand on principle or they can run after the money. But if they do the former they will benefit politically only if their fellow Democrats also take a stand on principle. They all are aware of this dynamic and few of them want to be the one left standing alone in the field. So a significant number of them go for the bucks because at least the money still gives them a chance of winning.
The Bankruptcy bill proves that the Democrats still have a long way to go before they start acting like a party again. No amount of feeling good about Democratic unity on Social Security can overcome the stench from this failure.