Members of the anti-war left who voted for Obama are by now utterly disappointed in the new administration if they have kept to their principles. But, as is explained on the American Conservative's Post Right blog, warmongering fits in perfectly well with progressivism and is indeed a "bipartisan tradition."
What should be even more troubling to those who call themselves progressives but oppose the current wars: Obama’s motivations for pursuing them are rooted in the central tenet of progressivism, enunciated by his idols, that the American national government is responsible for the reform and uplift of those “we” deem to be living below “our” standards, and that “they” must be protected from their oppressors. Obama’s role models followed the logic of that moral calling to the ends of the earth. ...
Of course, it is also worth mentioning that the conservative position is equally incoherent. Conservatives frequently deny that the government is wise enough to remake American society or the economy, but they somehow believe that we can transform Iraq and Afghanistan into Western style democracies.
War is the ultimate big government program. If you support war, you are supporting big government, and if you support big government, you are supporting war.
Indeed, I would argue that "conservative" support for war is the least-considered position in the right's pantheon of cherished ideas. Much like the unthinking support for the military found in much of the evangelical community, support for American aggression despite any and all potential problems with the stance is essentially a badge of honor for modern conservatives.