Ukrainian officials, defending their country against Russian aggressors, began doing something in July that seemed odd, even counterintuitive: They started speaking loudly and regularly about their plans to liberate Kherson—a key southern city that Russia seized only a week after invading Ukraine on February 24. Indeed, the Ukrainians telegraphed their intentions in a way that the Russians could not mistake. This was like waving a red cape at an angry, incompetent bull. Almost immediately, rumors proliferated that the Russians were racing reinforcements to Kherson to prepare for the Ukrainian attack. Goading the Russians into doing so seems to have been...