Xi Jinping once admired Vladimir Putin. Now he manages him.Russian President Vladimir Putin and Chinese President Xi Jinping attend a welcoming ceremony at the Great Hall of the People in May.Four years of war and economic isolation have reduced the Russian president to a supplicant in a relationship growing more imbalanced—and at times tense.Before Putin made his 14th trip to meet with Xi in China, he publicly signaled that the two countries would strike a breakthrough agreement on energy. Indeed, his May visit had no bigger ambition than persuading Xi to greenlight a second natural-gas pipeline between Russia and China—known…