If Xi delivers on growth-boosting reforms, and his U.S. counterpart President Joe Biden is unable to push through his proposals for renewing infrastructure and expanding the workforce, forecasts from Bloomberg Economics suggest China could grab the top spot—held by the U.S. for well over a century—as soon as 2031. But that outcome is far from guaranteed. China’s reform agenda is already languishing, tariffs and other trade curbs are disrupting access to global markets and advanced technologies, and Covid stimulus has lifted debt to record levels. The nightmare scenario for Xi is that China could follow the same trajectory as Japan, also touted as a potential challenger to the U.S. before it crashed three decades ago. A combination of reform failure, international isolation and financial crisis could halt China before it reaches the top. Another possibility—enticing to the skeptics—if China’s official GDP data is exaggerated, the gap between the world’s biggest and second biggest economies may be larger than it appears, and closing at a slower pace.