He denounced it as the "worst deal ever" during last year's presidential election campaign and dismissed it as an "embarrassment" to the United States in his inaugural speech to the UN general assembly last month.
On Friday, Donald Trump followed through with his threat to unravel the signature foreign policy achievement of the Obama administration, by decertifying the Iran deal, alarming allies and risking an incendiary reaction from Tehran.
The trigger was a looming October 15th deadline by which the White House was obliged to inform congress if Iran was in compliance with the deal. Under the 2015 agreement, the White House is obliged to update congress on Iran's compliance every 90 days.
Trump had reluctantly certified the deal on two occasions since assuming office, but there were growing signals in recent weeks that he would not do so a third time.
In the end, his administration stopped short of pulling out of the deal. While it did decertify the Joint Comprehensive Plan of Action (JCPOA), as the agreement is officially called, the deal is still, technically, in place.
Instead of killing it Trump has passed the ball to congress’s court, giving it the option of deciding to reimpose sanctions should Iran be deemed to reach certain “trigger points”, such as the expansion of ballistic weapons activity or support for terrorist activity.
Speaking to reporters ahead of the announcement, secretary of state Rex Tillerson said that the administration was not seeking to undo the deal, but to "fix" it.
Congress essentially now had three options, he said – to do nothing; to reimpose sanctions within 60 days, or to seek to identify those "trigger points" which would prompt the reintroduction of sanctions.
While the president favoured the latter option, Tillerson said there was no guarantee it would be achieved. “We may be unsuccessful. We may not be able to fix it . . . I think what he’s saying is, ‘Look, we’ll try.’”
Fiery speech
Key Republicans in congress have been in discussion with the White House on the issue over the last week, meaning that there is likely to have been some meeting of minds on the issue before today’s announcement.
Trump’s decision not to fully renounce the deal reflects a growing call from across the political world for him not to back out of it. Even strong opponents of the agreement – and there were many from both political parties in 2015 who strongly opposed the Obama initiative – believe that usurping it would be counter-productive.
Former Israeli prime minister Ehud Barak, a hardliner on Iran, urged Trump not to pull out of the agreement, believing it will help to legitimise Iran and potentially give Tehran a pretext for resuming nuclear activity.
But while the deal stands for now, the implications of Trump’s fiery speech and his dramatic rehashing of Iranian-US relations over the past 35 years, may have serious ramifications.
All eyes will be on how Iran responds, particularly the more hardline powers within the country, symbolised by supreme leader Ali Khamenei, who has handed over much of the political involvement in the deal to the more moderate president Hassan Rouhani.
The decision by Trump to impose sanctions on individuals and potentially entities associated with Iran’s Revolutionary Guard is also likely to enrage many in Tehran.
Similarly, the major shift in US foreign policy towards Iran has also alarmed America's allies, particularly in Europe. The US did not negotiate the deal bilaterally, but along with the four other permanent members of the UN Security Council plus Germany.
Limitations
The past few weeks have seen a major diplomatic offensive by European diplomats in Washington who have been stressing the need to maintain the deal. While aware of its limitations, the strong view from Britain, France and Germany, is that it was the best deal that could have been achieved, and has given weapons inspectors unprecedented access to Iran's nuclear sites.
They have indicated they are willing to work on the issue of “sunset” clauses – the fact that Iran can resume its development of nuclear weapons after 2025 – but that this should be part of a separate negotiation, not a reason to reopen the deal itself.
Similarly, they dispute the argument of sceptical Republicans that Iran has been slow to open up its military sites for inspection.
While Trump’s announcement has catapulted the world into limbo over the status of the nuclear deal, one thing that is certain is that his speech is likely to play well politically with his supporters.
Having railed against the Iran deal for months, Trump was not prepared to back down on his promise to revoke it, despite the advice of top advisers including Tillerson and defence secretary James Mattis.
His announcement on Friday allows the US president to prove to his supporters that he keeps his word, without fully pulling out of the agreement.
But the upshot is that, by usurping an international pact, he has moved the world one step closer to uncertainty and spawned consequences that may have implications for years to come.