Point out that lefty chicks are way hotter than righty chicks then drag his ass out to Seattle for the summer to prove it.

The thing about our current political all-stars is that they are all-star hypocrites.

I'd encourage him to learn the philosophy and learn how to analyze the politician's execution of the philosophy they claim to hold dear.

Being able to identify hypocrisy is good no matter which way you lean.

(pro-life vs cutting childhood health care)
(pro-life vs pro capital punishment)
(constitution touting vs opposition Islam)
(pro-free market vs anti-immigrant labor)
(etc. vs etc.)

Help encourage him to go to a normal college - or if not actually encourage him, help him pay for it or something.

Removing him from his family down there (probably where he is getting all of his opinions at age 15) and getting himself some education will do wonders for his stupidity.

It might not cure it, but I think its the best chance you will get.

Usually, a bout with poverty - real poverty with nowhere to go and no one to turn to - is enough to cure any Republican...at least for a while. If, however, one is hardwired for complete and total self-interest - as some seem to be - then there's really very little once can do about it other than try and neutralize it by being the opposite.

There are, of course, Republicans, who come from poverty, but they tend to forget the breaks and good luck they had climbing out of it and adopt the "if I can do it, so can someone else" attitude. Not everyone else is so lucky. And as Paul Newman once said, "If you don't think luck plays a part in success, then you are deluded."

Look for common ground first. There is a lot of it.

First, my sympathies.

I suggest you keep arguing with him. Don't lecture or talk down to him - debate, like you would with an adult. Consider his opinions seriously and respectfully (I know, it's probably hard sometimes), ask why he thinks what he does, and challenge his thinking. He'll be a better person for it, even if he doesn't grow up to agree with you, and he'll probably appreciate you that much more in the end.

Is he a reader? Make him a deal: you'll read a book by whatever conservative pundit he likes, if he'll read a book by someone you like. Then talk about what you read.

If you're already doing those things, I doubt there's much more you can do. I'm assuming you know better than to tell a 14-year-old what to think. Besides, my personal observation is that teenagers often go through a conservative phase, and they tend to think in very black-and-white terms. When he gets older, and (hopefully) takes a tour through the school of hard knocks, he'll probably mellow out. Also, as people age, they tend to gravitate toward the values their parents taught them. Are your parents are somewhat more progressive? If so, he will probably lean more towards the progressive side with time.

Buy him a copy of Atlas Shrugged so he can get through this phase as soon as possible.

I am very saddened to see that the majority of answers (as well as the question itself) are reflected in a way which state that opinions and beliefs other than those of a progessive/liberal mindset are demonized,crazy, ridiculed, or not tolerated.
What happened to the freedom to express and believe different points of view, ideas, and differences? I know many conversatives who are loving, open-minded, passionate and truly care about the future of our country just as much as anyone else.
I am tired of the meanness that seems to be growing ever so rapidly with the extreme left for those who dare to dissagree with them.
I've got friends and co-workers all around Seattle with varying degrees of political viewpoints, and guess what? We get along great because our relationship and respect for each other outweighs the differences.
Leave the kid alone, just accept & love him just as he is!