In light of the latest Petraeus '12 speculation (this time from Peter Beinart), Andrew Sullivan wants to know why everyone's so sure the General is a member of the GOP, wondering whether people are just assuming "that military = Republican." As best I can tell, the assumption that Petraeus is a Republican stems from the fact that he is. From Steve Coll's New Yorker profile of Petraeus:
Petraeus is registered to vote as a Republican in New Hampshire—he once described himself to a friend as a northeastern Republican, in the tradition of Nelson Rockefeller—but he said that around 2002, after he became a two-star general, he stopped voting.
Of course, that doesn't mean he's going to run. I thought the recent revelation that he'd been treated for prostate cancer--an announcement that came the day after a NYT front-pager speculated he might be keeping a low profile in the Afghan debate in order to run for the White House in 2012--was a sign of just how wary he is of being portrayed as a political, as opposed to military, leader.