China’s president, Xi Jinping, used to be the antagonistic one in the U.S.-China relationship. Since taking office in 2013, he has overseen the militarization of the South China Sea, increased censorship of Western content, and boosted regulation of Western companies. But Trump has turned the tables in a way previous administrations never dared, at least publicly. He invoked a third rail in China—Taiwan’s independence—in what he intimated was a bargaining tactic for tariff negotiations, yuan devaluation, and North Korea’s nuclear armament. Chinese officials were befuddled—about as much as Western watchers have been over Xi.