Why has Mr. Trump called it the “worst deal” and an “embarrassment”?
He has said inspectors from the International Atomic Energy Agency, the United Nations body that oversees compliance with the agreement, have insufficient monitoring powers. He has complained that some provisions in the agreement are not permanent, and that it failed to include restrictions on missile testing. He also has criticized the release of billions of dollars in impounded Iranian money returned to Iran’s control, describing it as a giveaway that has reduced American leverage.
How have other American politicians responded to Mr. Trump’s complaints?
That depends partly on whom you ask. Strident anti-Iran voices agree with Mr. Trump. But while many critics of Iran in the United States, both Democrats and Republicans, agree that the agreement has flaws, they also say it is better than nothing. Others fear that the United States would lose international credibility and alienate European allies if it renounced or undermined the deal.
They also point out that despite Mr. Trump’s denunciations, the International Atomic Energy Agency has repeatedly found that Iran is complying.
All the other parties to the agreement contend that it is working, and some of Mr. Trump’s own advisers have counseled him that it is in the interest of national security.
Why does Mr. Trump remain so hostile toward the agreement?
He pledged during the 2016 election campaign to scrap or renegotiate the agreement, which he said had weakened American security and appeased a longtime enemy of the United States and Israel. Moreover, under an American law, he must certify to Congress every 90 days that Iran is complying, creating for Mr. Trump a politically uncomfortable quandary four times a year.
When he last certified Iran’s compliance, Mr. Trump suggested it would be the final time.
Assuming he concludes that Iran is not complying with the agreement, he can take the formal step of decertifying Iran. That step would give lawmakers 60 days to decide whether to reimpose nuclear sanctions — effectively throwing responsibility for the agreement’s fate to Congress.
Does that mean decertification kills the deal?
No — or at least not necessarily. Iranian officials have suggested that they regard decertification to be an internal American political matter, as long as it does not lead to reimposed sanctions. And Congress might not reimpose them.
Would reimposed sanctions kill it?
Iranian officials have strongly suggested that they would abandon the agreement or at least no longer feel bound by its nuclear limitations.
At the same time, the Iranian government remains extremely reluctant to take such a step because it could jeopardize the economic relationships it has developed or revived with other parties to the accord, most notably in France and Germany.
Preservation of the agreement also keeps alive the prospect that Iran can purchase billions of dollars worth of Boeing and Airbus aircraft it has ordered under a provision of the accord that permitted such transactions.
Why can’t the agreement be renegotiated?
It may be possible, but Iran’s leaders have ridiculed the idea. Foreign Minister Mohammad Javad Zarif of Iran, who led the Iranian team that reached the deal in 2015, told The New York Times in an interview last month that the United States only wanted to renegotiate provisions it disliked. And if the United States withdrew from the agreement, he said, “Who would come and listen to you anymore?”