Four years ago Obama ran almost no negative ads on youtube. It was mainly about his aims, about the grassroot movement he wanted to establish, etc. Only very few times it was explicitly only about McCain. Now he's showing anti Romney clips on youtube which I don't really understand. Is he on the run? Instinctively, I would say, it makes more sense for the challenger to run negative ads against a president. The president himself should be more focussed on what he has achieved.