Branding against belief
True or not, I think that's going to be a hard sell. Branding the Repubs as obstructionist may be fairly easy, but rebranding the Democrats against the general (and well deserved) perception that they're chaotic and ineffectual will be really tough, especially in a midterm election where there isn't a single candidate to act as spokesman, mascot, or whatever.
They're going to have to graft Obama's image onto Congressional Democrats. It can be done. It's just very hard to brand against perception.