Sheriff: As with religion, the line is real world vs. not real world. Discussions of the government in some piece of fiction, whether published or PbP, aren't a problem. Real world politics, present day or historical, are inappropriate.
Just what is politics? As with religion, think broadly. If it has to do with some branch of real world government, whether international, national, provincial, local or whatever, it's better to avoid it. It's not limited to electoral politics, political electioneering or debate, or any other subset of real world politics.
Finally, when in doubt, err on the side of caution.