It more than just leans left. Most comments and posts from a conservative position get downvoted, and many libertarian ones do as well, while almost anything positive for liberals gets upvotes, even if it's not newsworthy.

I'd really like something like HN, but for political discussion. There are a couple okay subreddits, but it's just not worth it anymore IMO. I just want quality discussion about issues, complete with evidence. PoliticalDiscussion is okay so far, but then again, so was politics a couple of years ago.