Bush did one little thing that helped him wipe out any gains Gore had made on him in a debate. It happened when Gore walked up behind him and got way too much into his personal space. Bush turned around, eyeballed him up and down, and kept on. The audience laughed, and it was over for Gore for the night.
Perry will have a hard time, as it has been mentioned here, to come out swinging when almost every questions puts him on the defensive, or he's replying to constant attacks. That's obviously part of the game, but he won't shine too much in that situation.
The best thing he can do is keep his cool in that situation. People will compare him being cool-headed to Bachmann yelling insinuations that he's causing kids to be retarded.
I’m waiting for someone to have the gutts to tell Bachman that “retarded” in an offensive word. Having spent many years in the special needs community, I can say without question, that no mother would tell someone that her kid was “mentally retarded.”