I know how you feel. I have a Republican in my family and he is very smart but somehow has this "libertarian" blind spot. I have tried just about everything, but he is very well informed and can counter anything factual with ease.
So it comes down to philosophy at the end of the day and that is not unlike trying to tell someone that there religion is "wrong". It doesn't go over well at all.
It is worth continuing to point out the Republican ills when they are blatantly obvious in a kind way and just continue to plant those seeds of doubt. It's important that you don't "put it in his face" or make him defensive so he can just hear/watch the other perspective. John Stewart does a good job of amusing people while he shows how crazy they are.
Don't get him to defend anything... just keep up a slow drip of counter measures in the hope that he will see the light.
Good luck and thanks from all of us for trying.