China’s recent threat to impose sanctions on U.S. defense companies that sell arms to Taiwan should come as no surprise to American officials or corporate executives: Washington has been issuing sanctions of these sorts for years. It was only a matter of time before U.S. competitors started copying its tactics. Regardless of whether China follows through on its threat, Washington needs to be ready for a new normal in which the United States must defend against sanctions as well as impose them. China is taking a page from the sanctions playbook Washington developed against Iran. Between 2010 and 2015, the United States effectively gave companies a choice: If they did prohibited business with Iran, like buying oil, they would get cut off from doing any business in the United States.