Many Americans, of course, understand that China is on the rise and are anxious about it. Yet I also returned from my trip thinking that this American anxiety tends to be misplaced in one crucial way: China is not preordained to supplant or even match the United States as the world’s leading power. China’s challenges are real, not just the protests in Hong Kong but also the dissent in Xinjiang and Tibet, the bloat in its state-run companies and the looming decline in its working-age population.