There's a line of thought that is especially common among Bush supporters that claims that a policy is right or wrong independent of public support for the policy. I disagree with this opinion for a number of reasons, but in the case of wars, it is complete BS.
Basically, if a policy can only achieve its goals with sustained support from the public, then it can only be a good policy if there is reason to believe that the public will support it until those goals are achieved. Bush's Iraq policy was one of these policies, and he initiated the policy when it should have been clear that he did not have sufficient support to achieve the goals of the policy.
I laid out the argument in a comment on the Reason blog, and figured that I'd republish it here:
First, on the eve of the war, polls showed that support/opposition to the war was something like 60%/20%. Sure, it's a majority, but I don't think that it was enough to support a medium-size war. It probably would have been enough for an invasion of Grenada, but not an invasion of Iraq. For something like Iraq, I'd want to see a 5/1 ratio of support/opposition...especially considering that many of the supporters had weak reasons to support the war, and couldn't be counted on to sustain their support.
I say that support was weak because I don't think that many Americans would have said that they supported an invasion if the President hadn't already made it clear that he was planning to invade. Many Americans were simply giving the president the benefit of the doubt. Many Americans were also swayed by pro-war assertions that were blatently false to any informed person; as time goes on, we can expect the people to learn the truth and support for the war will erode to the extent that support was based on false beliefs. Two assertions in particular were problematic: Iraq supported Al Qaeda, and the transformation of Iraqi society would be easy.
Any reasonable person knew that Iraqi society would not be transformed overnight, and as time went on, the supporters of the war would realize that they'd been duped by the hawks, and support would evaporate. When support evaporates, it is impossible to complete the mission (whatever it was) and the whole thing falls apart.
That is the mark of a terrible leader, and that is what these new polls are reflecting.