There may be a problem with your assumption, the assumption being you are speaking to someone in a simple debate.
The man is not interested in debate, rather he is only interested in his own personal agenda. When he has one, he goes to great lengths to spread it, beyond emotion, beyond what a normal rational poster ought to do.
I'm relatively convinced he is one of two things. 1. He's possibly a Moby, who loves to sow deceit and division. 2. He's truly short a few parts in gray matter and emotional stability. A combination of these two is quite possible. Trying to be rational in the face of those alternatives makes no sense to me.
You can debate and give reasons till the earth runs out of oxygen, and you will get nowhere.
Insofar as his backing of Bachmann, if you have seen his posts then you know he doesn't back her as much as he simply backs anyone that will help his agenda to take down Sarah Palin. Bachmann just happens to be the reason du jour for him right now.
Nah - my assumption is that entering a debate will benefit others who read the posts - not the person I’m debating with.
Sometimes, the high road is what gets the interest of the undecided, and uninformed.
Have a great day.