I think we should allow questions on campaigning. For questions that are opaquely seeking campaign advice, we should probably worry more about the question being too localized.
I think many campaign advice questions will be caught by the normal rules of a SE website, but I think the main thing to be on the lookout for in questions seeking campaign advice is if they are a "what should I do?" question. Of course, that exact wording would be rare, but it can't be difficult to identify which questions are saying as much in different words. Politics.SE should aim to be descriptive, rather than prescriptive, and those questions call for the exact opposite of that.
I'm a bit hesitant to give a strict list of criterion, because I don't want to over-correct for an as-of-yet non-existent problem.
I haven't really participated much in the meta of any given SE site before, so I'm not really sure how communities normally deal with these sorts of issues.