If you do believe that her vote for Obama was out of ignorance then I believe that your influence after you marry will change that.
However, if you are passionate about politics and feel that you must share it with your spouse, then it may be a good idea to have a sit down with her and explain this. If she loves you and understands and agrees to at least appear mildly interested while you express your passion, then you have a keeper.
If it turns her off so bad that she breaks up, then you have discovered an incurable flaw in your relationship. Move on and find a young Ann Coulter. (and one not so skinny;^)