Vladimir Putin is clearly desperate. The question is whether this is good news or bad news. Another way of putting the question is whether it warrants a U.S. policy of exuberance or caution. The answer, in each case, is probably “a bit of both.” But the proper mix—how much exuberance, how much caution—is hard to calibrate. The Russian President revealed his desperation all too clearly in his Sept. 21 speech (which he’d originally scheduled for Sept. 20). He played it as a proud, nation-boosting, war-whooping address to the Russian people, but it came off as anything but. Advertisement He made...