“We must be prepared for worst-case and extreme scenarios,” Xi told China’s National Security Commission in May. He called on officials to “enhance real-time monitoring” and “get prepared for actual combat.” The sense of urgency may be heightened by the fact that Beijing is confronting some of its biggest challenges since Xi’s ascension more than a decade ago. Beyond the economic gloom, China’s relations with the West are increasingly tense. And unexplained personnel changes at the highest tiers of power — including the sudden removal in July of China’s foreign minister and two high-ranking generals — suggest that Xi may…