It is in this tribal context that all the factors Hanson describes here come into play. Bush isn't, in my view, a particularly proselytizing Christian, but to some apparently sincere Bush-haters he's Torquemada reincarnated. He isn't, actually, a particularly doctrinaire conservative (read FR for any 24-hour period for proof) but to his detractors he's Cotton Mather reincarnated. He is a far cry from the economic innovator that Reagan became but is portrayed as Mazarin all over again, intent on enriching a shadowy clique of insiders. All of these points are so fantastically exaggerated that one must wonder if their proponents aren't believing their own propaganda, and I submit that the latter is precisely the case - Michael Moore and his acolytes are a perfect example of this.
In short, they hate Bush because he is, in nearly every respect, not One Of Us. Clinton certainly was; his wife, She Who Is Not To Be Named, is as well. What we are talking about here isn't, in their obvious cases, any Eastern seaboard blue-blooded family-connect nonsense, but a total dedication to the ideals propounded by the left in the 70's. It is that class that finds itself in the critical position of taking power now or fading, through age, to impotent rage as the next generation of idealists comes along.
It is an axiom of politics that the wings of parties are more active politically than the remaining mass. Everybody knows that and usually discount the more activist speeches and actions. But now, because of the left shift, the activist left became much more mainstream left and brought with it its extremists' habits, like not just disliking the opponent, but actually hating him. This is an attitude that mainstream figures thought of as a bad taste to display, but now it suddenly became not just acceptable, but even fashionable.