This op-ed originally appeared in The Hill . Fulfilling a misguided campaign pledge, President Trump has chosen to violate the 2015 nuclear deal between the United States and its partners — the EU, U.K. France, Germany, Russia, and China — with Iran and reimpose U.S. sanctions that were waived according to the terms of the 2015 accord in exchange for severe limits and very robust international monitoring on Iran’s nuclear activities. Now, the valuable nonproliferation barriers established by the agreement, known as the Joint Comprehensive Plan of Action (JCPOA), are at risk. Contrary to Trump...