Chinese bombers and warships conducted exercises near Taiwan this month, a show of force that officials in Beijing called a warning not to pursue formal independence. Last year the number of Chinese air patrols off Taiwan’s east coast quadrupled, and Beijing under President Xi Jinping has stepped up pressure on the island democracy to “reunify” with the motherland.

China’s bullying is raising alarms in the U.S., which is obligated to help Taiwan defend itself under the Taiwan Relations Act. The mainland People’s Liberation...