Whether Trump ends up killing the nuclear deal or not, he has clearly signaled that he wants no reduction of tensions with Iran and no improvement in relations. He has unreservedly embraced the Saudi and Israeli view of Iran and the region, and is signalling his intent to re-establish American hegemony over the Middle East. Whether he can deliver on that promise or not remains to be seen, but the immediate effect will be two-fold:
Internally, the Rouhani faction in the Iranian government will be weakened, as their gamble on the nuclear deal leading to a less hostile American policy on Iran has failed. Iranian hardliners are already celebrating, with the head of the ultra-conservative daily Kayhan declaring that Trump has done them “great favors”.
Externally, Iran’s regional posture is likely going to get tougher, as the Iranian straregy is to meet pressure with pressure. Iran’s hardliners already believe that their policy in Iraq and Afghanistan has severely weakened the United States. If the U.S. doubles down on this regional posture, it will only further weaken Washington and as a result, undermine its ability to confront or isolate Tehran.
This intensification of U.S.–Iranian rivalry in the region was not inevitable. Had the Trump administration continued down the path of diplomacy prepared by the Obama administration, this rivalry—while never fully eliminated—could nevertheless have been tamed and the U.S.–Iranian relationship could have remained on a path characterized both by rivalry and by co-operation.