His expected decision to decertify the agreement
would allow him to save face and dent Barack Obama's legacy. And by handing its fate to lawmakers, he would also limit his political exposure to any decision to kill off a pact backed by US allies.
His expected move is already being condemned by critics, who warn he is putting US national security at risk to satisfy his own prejudices toward a deal he has branded an "embarrassment" to America
Trump has twice previously -- and grudgingly -- been forced to certify that Iran is complying with its terms.
Two senior officials told CNN that Trump is expected to unveil his decision next week. Nothing is ever set in stone with this unpredictable President, but he offered a glimpse into his thinking at the White House on Thursday night.
"The Iranian regime supports terrorism and exports violence, bloodshed, and chaos across the Middle East," Trump said. "That is why we must put an end to Iran's continued aggression and nuclear ambitions. They have not lived up to the spirit of their agreement."
Passing to Congress
If Trump goes ahead, it will not be the first time that the President has claimed what he sees as a political win and left it to Congress -- hardly known for taking tough decisions quickly under pressure -- with a political dilemma.
In September, Trump won plaudits from supporters by ending another Obama legacy item,
DACA, a program that shields undocumented migrants brought to the US as children -- and gave Congress six months to rule on their fate.
Trump's decision will not eradicate the Iran deal in itself: Republican hawks in Congress are thought unlikely at this stage to decide within a statutory 60-day period to reimpose sanctions that would cause Iran to walk away. European diplomats who support the deal don't believe that Republican leaders want to kill the deal, or carry the blame for doing so -- though there are no guarantees since the GOP vehemently opposed Obama's decision to sign on.
Still, some non-proliferation experts fear the decision could trigger a succession of events that weaken the deal, embolden critics in the US and hardliners in Iran who always opposed it, and lead to its eventual collapse.
"This approach could kill the agreement by a thousand cuts," said Kelsey Davenport of the Arms Control Association.
Democrats are already accusing Trump of indulging his political whims with no thought of the consequences. Architects of the deal also point out that it was limited to Iran's nuclear program, and was not meant to address Iran's threatening behavior in other areas.
"By not certifying Iran's compliance, even after the International Atomic Energy Agency confirmed that Iran is implementing its commitments, President Trump would jeopardize our security and national interests," said Democratic House Caucus Chairman Joseph Crowley of New York.
"It is clear that President Trump is focused more on continuing his campaign rhetoric than keeping Americans safe."
In opting to dent the nuclear deal, Trump would also reject the counsel of some top advisers, in the latest example of multiple differences splitting the national security team, that have most recently emerged in tensions with Secretary of State Rex Tillerson over North Korea policy.
"Absent indications to the contrary, (the Iran deal) is something that the president should consider staying with," Defense Secretary Mattis told the Senate Armed Services committee on Tuesday.
Sources told CNN's Dana Bash that Democratic senators visiting the White House this week came away with the impression that national security adviser H.R. McMaster was not sold on the idea that decertifying the deal was the way Trump should go.
Around the world
The move, despite available evidence that Iran is indeed living up to the pact, could also have a prolonged diplomatic cost.
It would be certain to outrage US allies and further jolt transatlantic ties that were soured by Trump's withdrawal from another international agreement -- the Paris climate accord.
It would raise doubts about American credibility in negotiations and threaten the country's capacity to close future global agreements -- for instance in any eventual diplomatic process to end the North Korea nuclear crisis.
The move could also allow Iran to claim the moral high ground by portraying itself as a reasonable player in the world in comparison to the United States.
Although he has frequently lambasted the Iran deal, Trump has yet to spell out his criticisms in detail.
But supporters of decertifying Iran say it will put the Islamic Republic on notice of a much more strident US approach that will target its activities throughout the Middle East and its ballistic missile program.
They also argue that the move will increase pressure on Iran and US partners and force them back to the negotiating table to fix what the Trump administration sees as the weaknesses of the deal.
"Until we take that preliminary step, which is still fully in compliance with the deal, I don't think our European partners are going to sit down and negotiate a hard bargain at the table. I don't think Iran is going to take the threat seriously," Arkansas Republican Sen. Tom Cotton said at the Council of Foreign Relations on Wednesday.
But critics say Trump's strategy will weaken the US negotiating position with European Union allies and Russia and China -- which have made clear they see no reason to reopen the deal and will not take kindly to US threats.
"The maximum point of leverage to address Iran's nefarious activities is now, before his expected terrible decision, not after, when he undermines America's credibility to uphold its commitments with our allies and partners," said a senior Democratic aide.