AP Photo

Don’t be surprised if the United States and China start rattling each other’s cages again, and this time, perhaps seriously. The Obama administration triggered this latest round by announcing on Friday a $6.4 billion arms sale to Taiwan. For Chinese leaders, this is the worst affront, since they consider Taiwan part of China. They retaliated immediately, mainly by announcing sanctions against unspecified U.S. companies involved in the arms sale. Similar byplay has occurred many times before, but never at a time when American fortunes seemed on the decline and Chinese prospects so bright—and never before with Chinese leaders at once so self-confident, even arrogant, about their international power, yet still so insecure and paranoid about their internal control over political and...