Wars can start quickly or slowly, but it is a dictum of strategy that once started, they take on a logic of their own. It is not too soon to think about how to bring this war to a close. The chances that Putin emerges strategically weak are real. But that does not mean the United States can win. It will have to settle for a picture that is much uglier than it was before the war, and the sooner Washington accepts that, the better.