"In 2006 polling, only about a fifth of Democrats recalled ever having supported the war, though in fact, almost half had supported it before the invasion."
http://www.theatlantic.com/doc/200801/partisan-retreat">It's in the middle of this article here.
But anyway at the time when it was obvious that the war was going to happen I thought that Bush was going about it in the wrong way entirely, but I believe I was mostly undecided about the war. Right after Bush actually invaded Iraq I turned against the war after hearing about how many billions the war would cost us.
It was around this time when it was obvious we would invade Iraq because Bush wanted to that I started to open up my eyes and slowly turn against Bush and the republicans. Before then I had blind loyalty to republicans/Bush simply from growing up in a republican household, and not thinking much about issues beyond "tax cuts = more money in our pockets, therefore they = good". At least I can say I was too young to vote in 2000, otherwise it would haunt me everyday knowing that I had voted for Bush.