On May 12, President Trump will have to decide whether to renew waivers of sanctions against Iran; if he does not, he will effectively be repealing the 2015 nuclear agreement. But, explains, Patrick Clawson, the deal will not simply disappear, and the complex network of U.S. and international sanctions that existed prior to 2015 will not simply “snap back.” The White House will instead face a series of decisions about how to proceed:
From a technical perspective, should the president terminate or fail to extend the waivers for the four pieces of legislation [that initially imposed sanctions on Iran], these statutes would immediately go back into effect, meaning the president would, in theory, be required to impose certain sanctions. In some cases, statutes explicitly direct the president to use [his] authority . . . to carry out such requirements, meaning the imposition of sanctions requires the executive branch to spell out how [he will do so]. However, a number of issues would need to be resolved before those sanctions would actually become effective again.
[Furthermore], a political decision will be needed about how vigorously to enforce the newly announced sanctions. Consider the record regarding the [1996] Iran sanctions act. The first sanction under that act was not issued until 2011: three presidents refused to implement it as written. . . .
There is also the question of how other countries, as well as Iran itself, will react:
Were the United States to trigger a snap-back of UN sanctions, the major European states may immediately register their political outrage, disappointment, or disapproval, but they would face a quandary about how to react in practice. On the one hand, some or all of the three European parties to the nuclear deal would be reluctant to be seen as cooperating with a Trump-led initiative to impose sanctions on Iran when they do not concur with either the U.S. judgment of Iranian noncompliance or the U.S. decision to restore sanctions. On the other hand, if Washington follows the letter of the agreement in its withdrawal from the agreement and places its action within the context of international law, including Security Council resolutions, the Europeans may find themselves handcuffed by their own professed respect for international law, as odious as the U.S. action may seem to them. . . .
Iran’s supreme leader, Ayatollah Ali Khamenei, who has the final say on all matters related to the nuclear deal, has . . . stated that . . . “if the threat from the American presidential candidates to tear up the deal becomes operational then the Islamic Republic will set fire to the agreement.” [However], Khamenei and other Iranian leaders complain regularly that the United States is already violating its commitments to lift sanctions, and yet Iran’s compliance with the deal has been in no way affected as a result.
Read more on Washington Institute for Near East Policy: http://www.washingtoninstitute.org/policy-analysis/view/tactical-issues-surrounding-a-u.s.-withdrawal-from-the-iran-nuclear-agreeme