I always thought George W. Bush's defining personal trait was the combination of ignorance and arrogance -- his contempt for experts and expertise, his belief that he really knew better. I've also always believed that Sarah Palin is simply George W. Bush, but moreso. Jacob Weisberg has a nice summary of Palin:

[T]he best Palinisms of all result when the huntress encounters something she wasn't hunting for—that is, when Sarah Palin comes into contact with most anything to do with domestic, foreign, or economic policy. It is this situation that generates those priceless let me tap-dance and, also, sing for you a little song while you think of a different question moments. One such was the juncture in her mind-boggling 2008 interview when Katie Couric asked Palin to name a Supreme Court decision she disagreed with, other than Roe v. Wade. Surrounded by hostile forces, out of cartridges for her Remington, she bravely held her ground and kept pulling the trigger, to no effect:
Palin: Well, let's see. There's—of course in the great history of America there have been rulings that there's never going to be absolute consensus by every American, and there are those issues, again, like Roe v. Wade, where I believe are best held on a state level and addressed there. So, you know, going through the history of America, there would be others. But, um.
Couric: Can you think of any?
Palin: Well, I would think of any again that could best be dealt with on a more local level maybe I would take issue with. But, um, you know as a mayor and then as a governor and even as a vice president, if I am so privileged to serve, I would be in a position of changing those things, but in supporting the law of the land as it reads today.
Tina Fey's caricature of Palin as an unprepared high-school student trying to bluff her way through an oral exam by mugging and flirting hit its mark not merely because of the genius of the mimicry, but because of its fundamentally accurate diagnosis of Palin as bullshit artist. Palin's exuberant incoherence testifies to an unusually wide gulf between confidence and ability. She is proud of what she doesn't know and contemptuous of those "experts" and "elitists" who are too knowledgeable to be trusted. This curious self-regard echoes through her book, Going Rogue, described by the critic Jonathan Raban as "a four-hundred-page paean to virtuous ignorance."