President Trump’s tariffs and other sanctions are hitting China at a vulnerable moment. The Chinese National Bureau of Statistics reported July 15 that gross domestic product grew by 6.2% in the second quarter, China’s slowest growth since 1992. The actual picture is much cloudier. Beijing has for years cooked the books to make the regime’s performance look better, and they are undoubtedly doing the same now.

No one outside the Chinese government knows exactly what is happening in China. But even the latest report concedes...