I think Joe Klein may be on to something in this article. It suggests that G.W. Bush's problem isn't that he lies but that he believes passionately in a lot of things that aren't true, even after a more reasonable person might conclude they are not true.
I dunno if this is true of Bush, but I think it's a characterization of him that could be very easily accepted by much of America. I have never bought most of the statements about the importance of "character" in our elected officials. It would be nice if we could judge them by such a thing but I really don't think anyone who runs around discussing what kind of man George W. Bush is (or Clinton or Gore or Cheney, et al) really has that much insight into the subject's true character. At best, they look at the image that his handlers manage to concoct, weigh it against the unflattering caricature that his opponents try to sell, and decide which they prefer to believe. That becomes the subject's "character."
Bush's backers are defending him against the notion that he lies. I think they can do that with some success. I'm not sure they'll be as able to dismiss the charge that he takes in bogus data that confirms what he wants to believe and refuses to question it. But I suppose we'll find out.