The consequences of withdrawing an agreement and whether renegotiating the agreement is a realistic option are an area of disagreement between supporters and opponents of the JCPOA.  Senator Chuck Schumer, a Democrat from New York, who opposed the agreement, urged the U.S. government to maintain sanctions, strengthen them and “rebuild the hard path of diplomacy, no matter how difficult.”  Senator Bob Corker, Republican of Tennessee, said he thought it was “hyperbole” to say that the agreement was the only alternative to war.  President Obama, for his part, argued that renegotiating the agreement was unrealistic and said in his speech to American University that “there is a better deal. … Relying on vague promises of hardness” and said: “Those who make this argument are either ignorant of Iranian society or they are not exactly with the American people. … Neither the Iranian government, nor the Iranian opposition, nor the Iranian people would accept what they would consider to be a total surrender of their sovereignty.  Obama also argued, “Those who say we can just walk away from this agreement and maintain sanctions are selling a fantasy.” Instead of strengthening our position, as some have suggested, the rejection of Congress would almost certainly lead to the lifting of multilateral sanctions” because “our closest allies in Europe or Asia, let alone China or Russia, will certainly not respect existing sanctions for five, ten, fifteen years after the diktat of the U.S. Congress, because their willingness to support sanctions in the first place on the basis that Iran ends its nuclear weapons efforts. It was not based on the belief that Iran could not have a peaceful nuclear power.  Foreign Minister Kerry joined these statements and said in July 2015 that the idea of a “better deal,” a kind of unicorn agreement, implies the complete surrender of Iran.
… it`s a simple and simple fantasy, and our intelligence community will tell you.   Senator Al Franken, a Democrat from Minnesota who supports the agreement, wrote, “Some say we would be able to negotiate a “better” deal if the Senate rejected the agreement. But I have spoken with representatives of the five nations who helped with the agreement, and they agree that that would not be the case.  German Foreign Minister Heiko Maas visits Tehran and says that Germany will not accept an agreement “less for less” on the implementation of the JCPOA. An INSTEX delegation is travelling with Meuse to discuss efforts to process transactions through the channel. April 2, 2015: Iran and the P5-1 announce an agreement on a general framework that outlines the general parameters of a nuclear agreement. The United States provides a more detailed fact sheet. Iran and the P5-1 agree to continue their meeting until 30 June to reach an agreement.
According to the Iranian fact sheet, Iran will temporarily and voluntarily implement the additional protocol in accordance with its confidence-building measures and ratify it within a time limit by the Iranian government and parliament (Majlis).  Trump`s unilateral decision to withdraw the United States from the JCPOA in May 2018 was quickly condemned by U.S. allies who have since struggled to find a diplomatic solution. On 5 January, Iran announced its withdrawal from the JCPOA. On the sidelines of the General Assembly, French President Emmanuel Macron meets separately with Iranian President Hassan Rouhani and US President Donald Trump. Macron tried to have a meeting with the two heads of state and government on his proposal to preserve the JCPOA, but Rouhani decided not to participate.