Introducing his running mate against the backdrop of the USS Wisconsin on Saturday, Mitt Romney flubbed his easiest line. “Join me in welcoming the next president of the United States,” he declared. There is no way to avoid reading this as a Freudian slip. Romney’s chief problem as a candidate has been his substantive vacuity, his failure to stand for anything beyond flexibility itself. In choosing Paul Ryan, he opted to outsource the content of his campaign to his opposite: a principled, conservative idea man. Ryan is now the head of the Republican ticket, Romney the body.