To challenge the power of his chief rival, the United States, Chinese President Xi Jinping, has linked arms with two anti-Western states, declaring a “no limits” partnership with Russia and pledging “unswerving” support for North Korea. But the specter of a budding bromance between Russian President Vladimir Putin and North Korean leader Kim Jong Un, after their meeting this week in eastern Russia, may not be as welcome a development for Xi as it might initially seem. Closer ties between Pyongyang and Moscow could result in both countries being less reliant on Beijing. That might diminish China’s perceived clout in...