Mark Halperin: This was not inevitable. It’s been an unpredictable year. There’s some laws of political physics. You run a lot of negative ads; you get the momentum back. Romney entered South Carolina with more money and with better organization. He didn’t have the momentum and the message. By the end, he had all four: He had the most money, the best organization, momentum from the debates, and the best message. And that made it a decisive win for him.