David Shambaugh is certainly prolific. His informative book “China’s Future” follows closely on the heels of “China’s Communist Party” (2008) and “China Goes Global” (2013) and fleshes out arguments first showcased in “The Coming Chinese Crackup,” a much discussed op-ed published in this newspaper a year ago. The George Washington University professor’s basic claim is easy to sum up: Unless the party’s general secretary, Xi Jinping, introduces major political reforms, the economy will tank and the party will crumble. Being too careful a scholar to express certainty about the exact timing of these events, Mr. Shambaugh...