There was a deal with Iran that the United Sates had called the joint comprehension, plan of action(JCPOA) which included China, Russia, France, UK, Germany and the USA, there may have been some flaws with it, but flaws that could have been renegotiate with all those other countries on our side and included in the deal, why would someone (Trump administration) tear it up and give Iran free range and then go in and spend billions and billions, if not soon a trillion, to get back a fraction of a deal that we already had and one that we are in alone with now.