It's possible to have civil political discourse, but it takes a lot of effort, much more than maintaining the entire rest of a site. You can't do it by tweaking things here and there, you need active moderators who can maintain cool heads themselves about topics they are passionate about.
I don't think it's worth HN spending that effort, and what's more important it doesn't look like HN wants to spend that effort.
If you want a swimming pool, you have to maintain it. If you can't, fill it in. HN should either invest a lot more maintenance on political posts, or take a very very heavy ax to them.