Maybe you can refresh my memory, but has there ever been a time when a significant number of Democrats ever bucked their system? Republicans will do that, and have done it often, but Democrats seem to be in lock-step with each other. In addition, I've heard that Pelosi contributed to a number of candidates, thereby pretty much owning them for the next two years.
The Democrats haven't been in this position in decades. There's no guarantees they'll get reelected in 2008, and they've been out of power on the Hill for over a decade. If people think the Democrats put partisan spoils ahead of the security of the US, they will be out of power in two years. The Bluedogs know this.