The strategy is obviously to keep Bush on the defensive by making wild accusations that he must defend against...even if they're untrue. Most people will hear the accusation but not the rebuttal.
And we watch the media (including Fox) run full speed ahead from the perspective of the DNC. Time and time again.
It is the DNC that is dictating the terms of the accusation and the type of proof required to rebut it. Once that proof is offered, they simply move the goal posts and the compliant media says "Yeah, what about THAT?"