"The U.S. dollar is the linchpin of not only the American economy but also the world monetary system." Those words were the lead of an editorial in this newspaper on August 21, 1978, amid the inflation of the 1970s and the world's last great dollar crisis. Are we watching another such period today? It's not inevitable, but this week we all got a reminder of what such a thing looks like, and it isn't pretty.

The dollar is "losing its status as the world currency," declared Xu Jian, a middling official at China's central bank,...