If you write a political poem, there is a good chance that it will lose its topicality, or at least become somewhat dated, by the time it gets published (if indeed it does reach that fortunate end). I am thinking of a poem or three of mine which have , because contexts have shifted somewhat, gone past their political "due date" languishing for months in slush piles of various magazines. The slowness of reviews to consider, accept, and publish work acts itself as a sort of censor. This aside from the unwillingness of many reviews to venture into unsafe territory (call it middleclassness, apolitical bias, what you will.) If you need to rush a poem into print so that it have the impact of timeliness, you have to be either some kind of celebrity (at least in the poetry world), or lucky. The alternative is self publication -- blog or otherwise -- with its inherent limitations.
P.S. This post provoked some good discussion which has helped clarify my own views on this subject. Just click on "comments" below... Bravo, Rob, Andrew, Jill & Pearl!