I would moderate it like pg does here. High-quality political articles only and moderators would remove inappropriate content. Partisanship may come into play, but only in the article rankings via votes.
You would need a large number of like-minded moderators to manually remove off-topic articles and idiotic comments.
It's hard enough for HN to keep a high level of discourse. A community based around politics will attract partisans and weigh heavily against people's identities. Eventually one group or another will reach enough critical mass to bring the site to one political center or another, and it will be socially impossible to stray too far from that center. Most forums get around this centering problem by explicitly declaring a center. HN does this implicitly by centering around pg's views--a programming social news site founded by Jeff Atwood would have a much different bent.
Likewise, political forums either implicitly or explicitly center around left-wing, right-wing, libertarian, feminist, socialist, or some other default viewpoint where there may be a core community of e.g. leftists, and right-wing commenters who show up to the fight are something of a different social group than the core of people who agree with the site's ideological bent. (Huffington Post comes to mind).
It's a hard and interesting problem though, so if something comes of this discussion I'd be glad to help.
