I find it funny that so many people bring up JFK. All accounts I have heard of him refer to him being somewhat of a transformational president, but below average as well. I have yet to hear somebody call him a good or great president.
I remember Bush Sr. and Reagan being very dignified presidents from my early years- I don't remember much at all about Carter other than not understanding the whole hostage crisis issue (and I remember a wild celebration in my homeroom class the day they were released).
At least from what the movie portrays, George Bush Jr. seems like he was a decent man who had a vision of how the world should be- that vision was used by his cabinet, particularly the vice president (and this is going from the movie, sine we'll never know) to do some pretty bad things. All in all, I can't find a person that can name a republican president that did a poorer job in office than Bush Jr. did. Not all of it was his fault, but it is what it is......