Matt has a pretty sharp take:
Given that they're all viewed skeptically by cultural conservatives, the only possible way for any of them to campaign for the nomination is with an escalating race to the right on national security, even though Iraq just led the GOP to disaster last November. Which vulnerable state that Bush won in 2004 is rendered more secure by making the Republican Party less committed to social conservatism but more committed to the Iraq project? Ohio? Virginia? Missouri? Nevada? Iowa? I don't see it. But only a real conservative Christian can afford to put even a ray of sunlight between himself and the president on the subject of Bush's massively unpopular war, and the cult of celebrity has left the GOP's top-tier field without one.