The key to getting along with people that you don't agree with in politics is to be respectful, talk about what you know and ONLY what you know or can back up with facts that are verifiable by both parties, and believing that both sides have something of value to add to the conversation as well as their good intent.
The reason political discussion devolves so quickly here and in other places is that people want to assume harmful intent (which is ridiculous and against the basic nature of human psychology) or they take a combative stance on everything and treat it like a battle which must be 'won'... which is also ridiculous and wholly arrogant.
The couples like this who disagree on matters political can only work because they know that the other person is a good and loving person, regardless of possible flaws in their ideals.