You can't win an argument with a partisan

You can't win an argument with a partisan--left or right--because their reasons aren't their real reasons, even when they believe them to be consciously. When you attack their spoken reasons, then, what actually happens is that they identify you as a member of an enemy tribe, who must be defeated. Research has shown that refutation of even crazy stuff like Obama being a Muslim agent achieves nothing.

It's not all hopeless, though. Both sides have valid points. The trick is to acknowledge and validate those. That may get you out of the "enemy tribe" category in their heads. And give you a chance to redirect their valid concerns to different targets.

You also have to acknowledge your own party's screw-ups, even though this will trigger your own tribal desires to defend-your-side-at-all-costs.

And you can get through their defenses with ploys they don't expect.

For example, this election is going to be a disaster for Republicans. Since the Republican Party is p0ised to win big, you'll sound like a left wing loon by saying this. But then you say that of course the Republican Party--fueled by secret money funneled into nonprofits that aren't supposed to engage in politics but do anyway--will win big. But that just means that Republican voters are voting the foxes back to take charge of the henhouse.

The point to make here is that the GOP is run by con artists who have almost nothing in common with Republican voters, and who hold them in contempt, just as Jack Abramoff held his Indian clients in contempt. You also have to acknowledge the Democratic voters face a similar problem, but that we have to choose between these alternatives, and it's the GOP that has proven, time after time after time, to be even more fiscally irresponsible and less devoted to the very freedoms they yammer about in public.

Lastly, you can try to enlist them in supporting nonpartisan reform measures like nonpartisan redistricting, proportional electoral college representation nationwide, and voter contribution source transparency.