Rejection of the nuclear deal would collapse the sanctions regime and damage U.S. reputation as a leader for decades
Rejection of the agreement would severely undermine the U.S. role as a leader and reliable partner around the globe. If Washington walks away from this hard-fought multilateral agreement, its dependability would likely be doubted for decades.
Rejection would also destroy the effective coalition that brought Iran to the negotiating table. China and Russia would likely resume trade with Iran. U.S. allies, unsettled by Washington’s behavior, would move their own separate ways.
The other five negotiators would likely have little stomach for going back to Iran “for a better deal.” The ambassadors of the five countries recently assured members of Congress that their governments would not return to the negotiating table should Washington reject the agreement.
Future sanctions would then have to be largely unilateral U.S. efforts — and less effective. There would be no coalition standing by to restore sanctions or apply other pressures if Iran did not comply. It would also be difficult to develop joint forceful action against Iran should it decide to go for a nuclear weapon.