"Supporting" change is not the same as "effecting change". Real change isn't going to be achieved by voting for minority candidates, at occasional elections every few years, it's only going to come by the work that gets done in between the elections. As Joe Hill would have said "Don't vote, organize".

What voting can do is help make it a better environment for that organising, or a worse one. And from all I've heard, I can't envisage that Bush getting back will achieve anything but reduce the room for that kind of organising.

And radically minded Democrats are surely going to be much more inclined to get involved in that kind of hard work in the situation where they are disappointed by a Democrat administration that fails to deliver what they hoped it might deliver, than they would be in the setting of a new Bush administration, which would just their reinforce their dream that somehow a Democrat victory would solve everything.