With the world preoccupied by the coronavirus pandemic, China has been looking to exert more military control in the South China Sea. This week three warships from the U.S. Seventh Fleet, joined by an Australian frigate, responded by sailing into the disputed waters in a show of force. The danger is that Chinese naval officers misread America’s public mood and think they can embarrass the U.S. without escalation.

The South China Sea is a critical waterway in the Western Pacific, bordered by Taiwan, Vietnam, Singapore, the...