Let's tell the truth: Putin is doing what he is doing because HE KNOWS THERE IS WEAKNESS IN AMERICAN LEADERSHIP.
I also believe, whole heartedly, that if Mitt Romney were in the Oval Office, these actions--if Putin took them at all--would have been followed by real, true, consequences.
My gut feeling, though, is that Putin wouldn't have done anything like this...because Romney, whatever else he was, wasn't promising to be "flexible" for Putin.