While you can't judge a book by its cover, the artwork adorning David Shambaugh's "China's Future" says it all: It transmogrifies the national flag into a giant question mark.

No question matters more to economists, businesspeople or the next U.S. president than where the most populous nation might find itself, say, five years from now. Its answer holds the key to everything from global growth to geopolitics to investment returns to climate change. And Shambaugh's crack at offering one is anything but comforting.

China probably won't collapse, the long-time Sinologist concludes. But it's already ensnared in the dreaded "middle-income trap" President Xi Jinping pledged to avoid. That's when a developing nation reaches a relatively comfortable per-capita-income level (say, $10,000), but can't make the great leap forward into the big leagues of wider prosperity. And for Xi's China, it's a crisis all its own.