This started off as a comment.
When I argue politics with my Republican Dad, I focus on a position that he feels strongly about, which is Veterans care. He is a Vietnam vet and so I bash him over the head every time we talk about how Bush is slashing Veteran's benefits, refusing to give armor, paying mercs 100K to drive trucks full of "sailboat fuel", and anything else I can remember.
I never let him get the last word on these topics, I always leave him with a clear-cut image that Bush is against Veterans.
Then, I also tell him the latest Republican hypocrisy every time we meet. However, I think the thing that finally sunk the ship was this. He always says that Democrats are just as bad as Republicans, just as dirty, just as unethical, just as self-serving. I was in the car with him and we had the following conversation: