I have a colleague like this. She is very right-wing and will often make political comments out of the blue, usually very derogatory to liberals or the current (or past Democratic) administrations.
I hate being confrontational and for a long time would just ignore her comments. After a while I got the feeling that she thought we were on the same page politically, as the comments only increased.
Finally, one time, I commented on something she said that I agreed with (believe it or not!) and said something along the lines of, "Well, you know I'm a liberal on most things, but..." etc., etc. putting my two cents in.
Another time when there was something we really disagreed on, I said, "Well, you know I'm a Democrat, so I'm not really on board with that." I just kept clearly identifying my stance without overly engaging in the discussion or stretching it out.
I think once she realized I was on a different wavelength, she backed off on the political commentary. She still does it from time to time, but she is respectful enough of me not to yammer on or try to force her views down my throat. For my part, I don't mind hearing a different point of view once in awhile - I just don't like being hammered over the head with it and I REALLY don't like arguing politics. 9 times out of 10 it's a useless battle.
Keep in mind that there are some people out there who, once they know you are of a different mindset, just LOVE to keep the argument going and push your political buttons. That type of person needs a firm "Sorry, but I don't discuss politics!"
Good luck!