China has become comfortable pushing around American companies—a little too comfortable. Its boycott of the National Basketball Association’s Houston Rockets, announced Sunday to muzzle support for mass protests in Hong Kong, has alerted Americans to the threat posed by China’s bullying in a way that intellectual-property theft never could.

“Fight for freedom. Stand with Hong Kong,” tweeted sports-analytics whiz Daryl Morey, the Rockets’ general manager, on Sunday. Within a few hours, Mr. Morey had deleted the tweet, team...