The question of Iran's changing its response to the United States' withdrawal from the nuclear deal is no longer whether but when. Iran initially took a pragmatic approach to the news, predicated on other countries' willingness to push back against Washington and continue purchasing oil from the Islamic republic after U.S. sanctions go back into effect Nov. 4. But that outcome now looks unlikely. As a result, Iran will shift to a more aggressive response, including perhaps pulling out of the Joint Comprehensive Plan of Action (JCPOA) and even restarting its nuclear program to gain leverage in future talks with the United States. The Sting of Sanctions For Iran, the writing is on the wall . The U.S. sanctions against it have teeth, and so far, most U.S. allies seem reluctant to defy them.