I think you need to talk with him about what it means to be a person. Are people more than their political positions? If so, what is this “more” that goes beyond the political? Does he see these other important qualities in you? I think he needs to broaden his perspective that human beings in their importance transcend politics. This is not easy to learn and so he and you will have to work on this more transcendent perspective. As you forgive, try to see these larger human qualities in your partner. Such a wider perspective likely will help you in the forgiveness process.
For additional information, see Forgiveness for Couples.