If you use "Bush" and "Kerry", you will already be dealing with a biased subject.

I would suggest you create some neutral source with a demographic section to guage pre-dispositions - like attendance in church, kids/no kids, income, home ownership, hours spent wasting their lives watching "reality tv" and stuff like that. Then expose them to a crafted set of releases and see how much they change their mind from the original neutral source test.

What is your budget? Or is this just a hobby? What is YOUR agenda?

Good luck.