This write-up in the Post has a lot to recommend it, and I second the idea that fundamental to Bush's unpopularity is that he has few big-picture policy ideas to propel him, and the ones that he does have are dead letters.
This is what I know about America: we're an inspirational country. And what I mean by that is that we are and always have been driven by inspiration. Look at the language in the documents that created the nation. The Declaration of Independence inspired a diverse collection of colonials with varied notions of self-interest to rally around the idea that we should be free of British rule. The Constitution and Bill of Rights are perhaps the most inspirational political documents ever crafted, and even more magically, Americans on the whole continue to believe in them with a fervor that could stun the most zealous religious adherent. We are a people hypnotized by the language of aspiration, living out a fantasy dreamed up by hopeful aristocrats centuries ago. It's an amazing thing, this America.
But George Bush doesn't have any inspiring dreams to offer as his tenure wanes. Privatize Social Security? It never did better in the polls than he does now. A free Iraq? I think we all hope that one day roses will bloom in Baghdad, but anyone who was holding his breath for it expired some time ago.
George Bush is a tiny president with tiny dreams for his country.