An obvious tactic
As Calpundit points out in this post, the Dems should really get off their stupid intra-party-squabbling butts and start hammering home, again and again, that Bush is A LIAR. A non-stop, 24/7, lying liar who lies. And Dick Cheney, too, as his recent hilarity-inducing appearance on Meet the Press only proves. Real "pants on fire"-degree lies. If they would just start saying this, over and over, and hold up the proof, the press would have to start conceding the point. In fact, they already are. I'll see if I can't find the link to the story, but Tucker Carlson, not exactly a Democrat, spoke to Salon about the fact that Bush and Co. will simply "lie, knowing that you know that THEY know they're lying, and they'll lie anyways."
We live in a Banana Republic.