The president is reportedly planning on decertifying the deal - a move that would give Congress 60 days to determine whether to reinstate sanctions against Iran removed under the agreement.
He said on Thursday: "We must not allow Iran.to obtain nuclear weapons". Broadly speaking, they do not think the economic benefits have lived up to projections, in part because the USA government has not enthusiastically driven business to post-sanctions Iran. What storm? and in what part of the world? are the questions Trump's cryptic comment triggered.
According to press reports, Trump seems inclined not to certify Iran's compliance with the agreement, although he could leave that decision in the hands of Congress.
White House spokeswoman Sarah Sanders also declined to say what Trump meant.
If Trump takes steps to abandon the nuclear deal, he would be going against the advice of his top national security leaders, including Secretary of Defense Jim Mattis and Joint Chiefs Chairman General Joseph Dunford.
"The point I would make is that if we can confirm that Iran is living by the agreement, if we can determine that this is in our best interest, then clearly we should stay with it", Mattis told a Senate hearing. It is unclear if the president's statement referred to his coming action on Iran. But that in itself is a risk; and in any case, Mr. Trump's expression of displeasure with the agreement can only alienate this country's closest allies, which worked so hard to get a deal.
The next certification is due on October 15.
The deal is also contentious inside the administration.
Trump hinted at what might be "necessary" during his inaugural address before the United Nations General Assembly last month, in which he threatened to "totally destroy" North Korea in defense of the USA or its allies.
Earlier, Trump issued a national security memorandum aimed at integration, sharing and use of national security threat actor information to protect Americans.
"Not just the nuclear deal as bad behaviour, but the ballistic missile testing, destabilising of the region, Number One state sponsor of terrorism, cyber attacks, illicit nuclear programme", Sanders continued.
"Iran has in all bilateral diplomatic meetings ... emphasized that its defensive missile program is not negotiable", and does not violate a Security Council resolution endorsing the nuclear accord, the Iranian Mehr news agency quoted Foreign Ministry spokesman Bahram Qasemi as saying.