This one isn't really an issue for me because I'm not political at all. I tend to vote Democratic because I like their more liberal policies. But, I'm not opposed to listening to other people's points of view. I think that's where we go wrong in society, refusing to listen to other people's perspectives and assuming that only we have the right answers. But some people are pretty set in their ways and beliefs so I'm not surprised to see this is something that would cause strife in a relationship.

I guess it would have to depend on their reasoning. I'm a pretty staunch Democrat, but my father is a lifelong Republican, so I've learned how to deal with political difference. It's always nice to have a hearty debate if the other person has done his or her homework and isn't just spouting off whatever they happened to hear on Fox news.
There are a lot of couples who have made inter-party relationships work. Look at Arnold Schwarzenegger and Maria Shriver.