I think a more productive conversation to have with your therapist than vetting his particular politics would be to explore with him this idea that a certain viewpoint or set of opinions about anything would constitute the unforgiveable sin over which you would terminate, despite everything else you two have experienced together.
Well intentioned people can fall on either side of the political aisle, and politicians are faced with a lot of things that most of us are unaware of. I think part of the issue with political discourse in our country is just how black and white the dominant thinking, regardless of political affiliation, has been lately. Black and white, all or nothing thinking is a trauma response, so well worth bringing to therapy and processing through when we encounter it in ourselves.