Look closer, however, and China’s future doesn’t seem so bright. Once-torrid growth had already slowed dramatically before Covid-19 compelled the government to lock down major cities indefinitely. Water, farmland and energy resources are becoming scarce. Thanks to the legacy of its one-child policy, China is approaching demographic catastrophe: It will lose 70 million working-age individuals over the next decade while gaining 120 million senior citizens. And whereas the outside world once aided China’s rise, now advanced democracies are kicking Chinese firms out of their financial markets, strangling China’s tech giant Huawei, boosting military spending and creating multilateral coalitions to check Beijing’s expansion. Mr. Xi may tout the rise of the East and the decline of the West, but behind the scenes, Chinese government reports paint pessimistic pictures of slowing growth at home and surging anti-Chinese sentiment abroad.

In the long term, China’s woes will make it less competitive. It probably can’t outpace America in a superpower marathon, let alone America plus its allies. But in the near-term, we should expect a more dangerous China—one that gambles big to reshape the balance of power before its window closes…

Meanwhile, U.S. military power is about to dip. The mid-2020s will witness the mass retirement of aging U.S. cruisers, guided-missile submarines and long-range bombers, leaving the U.S. military with hundreds fewer missile launchers—the key metric of modern naval firepower—floating and flying around East Asia. While Washington, Tokyo and Taipei are all undertaking much-needed defense programs focused on denying Chinese hegemony in Asia, those efforts won’t bear fruit until the early 2030s. Mr. Xi has repeatedly said that the task of “liberating” Taiwan cannot be passed down from generation to generation. In the mid- and late 2020s, he’ll have his best chance to accomplish that mission.

If war comes, it is likely to feature the massive application of force. Beijing could theoretically try to coerce Taiwan into unification with a more limited operation, such as an air-sea blockade or the seizure of Taiwan’s small offshore islands. Yet none of these options can guarantee Taiwanese capitulation, and all of them would give Taipei, Washington and other democracies time to mount a punishing response. To achieve its goals, China has to go big and brutal from the start.