Bloomberg | Nick Wadhams: Donald Trump has railed against the Iran nuclear deal since it was agreed to in 2015. As a candidate, he said undoing it would be a top priority as president. As president, he�s called it one of the worst deals ever. The UN General Assembly session in September was a chance for him to make his case to the world and persuade allies to get behind an effort to rewrite the accord and impose stricter controls on Iran. Yet after a week of speeches, backroom negotiations, and top diplomatic meetings, the U.S.�appears more isolatedand its allies more united around the importance of the agreement. The week also exposed the administration�s internal division over Iran�and disdain for the details of the accord.

On Sept. 20 at the UN, Secretary of State Rex Tillerson laid out to European and Iranian leaders all the things Trump hates about the nuclear deal, chiefly that its main restrictions do nothing to address such issues as Iran�s development of ballistic missiles, its support for Syrian President Bashar al-Assad, and its backing of terrorism in the region. After the meeting, it became clear the two sides were talking past each other. France and Germany insist the agreement, imperfect as it is, does what it intended to do. Iran�s nuclear program is contained, so why blow up the deal? The U.S. says by focusing on the details, its allies are missing the bigger picture. While grudgingly admitting Iran is meeting the letter of its obligations, Tillerson has resorted to arguing that the nation is �clearly in default� of the accord�s preamble calling for progress toward regional peace and stability.

Trump has until Oct. 15 to tell Congress, as he�s required to do every 90 days, if Iran is complying and if the deal remains in the U.S. national interest. He announced at the UN that he�s made up his mind, and while he�s not saying, it�s�generally believed�the U.S. will decertify Iranian compliance, kicking the issue to Congress, which must then decide whether to reimpose sanctions.

According to officials briefed on Trump�s thinking, he wants to use that threat as leverage to enact sanctions that would isolate Iran�s economy as much as it was seven or eight years ago. To get there, the U.S. would need European allies to participate. That�s a big gamble considering those countries are talking about protecting their own companies if the U.S. reimposes sanctions. �I have no doubt that if this scenario materializes, which it�s not clear it will, the European Union will act to protect the legitimate interests of our companies with all the means at our disposal,� David O�Sullivan, EU ambassador to the U.S., said on Sept. 25. That could end up isolating the U.S. rather than Iran, which has promised to stick to the accord if the U.S. withdraws. �The Trump administration has not explained how this policy will work better, what this strategy will actually achieve, and how Washington is going to implement it,� says Kelsey Davenport, director for nonproliferation at the Arms Control Association.

One of the proponents� frustrations is the amount of time they�ve spent educating U.S. officials on what the deal does and doesn�t do. Officials with the�International Atomic Energy Agency, the Vienna-based body charged with verifying Iranian compliance, had to walk U.S. counterparts through the basics, according to three senior diplomats with close contact to the agency. Yukiya Amano, head of the IAEA, had to explain that agency monitoring doesn�t cover Iranian support for Hezbollah and meddling in the region. IAEA also denied administration appeals to reveal classified data collected in Iran, say the diplomats, who spoke on condition of anonymity.

Tillerson�s task is complicated by internal divisions. On Sept. 26 the chairman of the Joint Chiefs of Staff, General Joseph Dunford Jr., questioned backing out of the deal because it might weaken U.S. credibility in any talks over North Korea. There�s also Tillerson�s friction with Nikki Haley, the U.S. ambassador to the UN. On Sept. 5, Haley�gave a speech�to the American Enterprise Institute on the Iran agreement in which she made several errors, including her claim that the deal was meant to end Iran�s nuclear program entirely. In keeping with Haley�s belief that her cabinet-level rank means she doesn�t report to Tillerson, she didn�t consult with him or his staff.

The tension boiled over at the Sept. 20 diplomatic meeting at the UN to discuss the Iran accord. Haley wasn�t originally invited, but�at the last minute, she took a spot reserved for a senior adviser to Tillerson without asking the State Department. She then tried to sit at the main table in a space reserved for another U.S. official but was told to sit in the back, according to two people familiar with the situation. Haley�s office called that version of events false and said she participated with encouragement from the White House. To cope, Tillerson is leaning on skills he learned during 40 years at�Exxon Mobil Corp.��As a longtime negotiator, I learned to never say never,� he said at a Sept. 20 briefing. �And second, it always gets the darkest before you might have a breakthrough.� �With Kambiz Foroohar