Even if the US stays in the deal -- which US security officials, European allies and the UN say is working to limit Tehran's nuclear program -- Trump's move will have any number of ripple effects, said critics and experts, who point to a loss of US credibility, the message it sends to North Korea, and possible retribution from Iran, among other things.
"From an international perspective, walking away from the deal undermines US credibility internationally and will discourage other countries, such as North Korea, from resolving their disputes with Washington diplomatically," said Ahmad Majidyar, director of the Iran Observed Project at the Middle East Institute.
Trump made the long-anticipated announcement at the White House on Friday, essentially handing the problem to Congress, which now has 60 days to decide whether to re-impose sanctions that could leave the US in violation of the agreement.
If lawmakers fail to address what Trump called the international agreement's "many serious flaws," then it will be "terminated," he said. In the meantime, Trump said the US would get tough on aspects of Iran's behavior that aren't covered in the pact.
Trump supporters such as California Rep. Devin Nunes, chairman of the House Intelligence Committee, say the announcement and decision to further penalize the Iranian Revolutionary Guard Corps for supporting terrorism will send a "strong" message.
Others see a slew of unintended consequences.
Undermining US interests
They point to the potential for asymmetric retribution from Iran, including the targeting of US allies and US troops and diplomats in Iraq, Syria, Yemen, Lebanon and elsewhere. Tensions between the US and Iranian naval forces in the Persian Gulf could further increase.
Majidyar notes that the Iranians had been "hinting that the Revolutionary Guards would step up efforts to undermine US interests in the region," including targeting counterterrorism and stabilization efforts in conflict zones such as Iraq and Afghanistan, if Trump made good on his threats to leave the deal.
Indeed, the head of the Atomic Energy Organization of Iran warned that any action to designate the IRGC as a terror group "is tantamount to a declaration of war," the semi-official Tasnim news agency reported on its English language website Friday.
The report also referenced comments from Sunday by IRGC Commander Ali Jafari saying that if the US administration's "stupid decision" to designate the IRGC as a terror group is true, the IRGC will, in turn, treat the US military around the world -- particularly in the Middle East -- as if they were ISIS fighters.
Others say Trump's decision will affect the US ability to deal with North Korea's nuclear program.
Former diplomatic negotiators ask why Pyongyang should even consider the prospect of diplomatic talks with an administration that rips up nuclear deals. They add that Trump's announcement also makes it that much harder for US allies and security partners to vouch for Washington.
Wendy Sherman, a former Under Secretary of State who has handled negotiations with Iran and North Korea, noted that Trump is headed to China next month.
He'll be "wanting China to be tougher with North Korea, get North Korea into some serious dialogue," Sherman said. "China will be in a very difficult position to say to North Korea, 'well you should in fact sit down with the Americans,' when in fact the Americans have just put a deal at risk to make sure that Iran doesn't obtain nuclear weapons."
The decision will strain relations with Europe, many expect, and potentially offer Russia, China and Iran an opening to vie for greater influence there and elsewhere.
"The transatlantic alliance is going to be wedged by Iran, Russia and China, putting them in a more powerful position, us in a less powerful position," Sherman said.
Secretary of State Rex Tillerson said Friday that he expected European allies "are going to be very supportive in efforts undertaken to deal with Iran's threats." But privately and publicly, European diplomats express frustration and say they're not interested in following along.
"We cannot afford as an international community, as Europe for sure, to dismantle a nuclear agreement that is working and delivering -- especially now," EU Foreign Policy Chief Federica Mogherini said Friday, in Brussels. Noting that it's a multilateral agreement, she added that, "it is clearly not in the hands of any president of any country in the world to terminate an agreement of this sort."
"The President of the United States has many powers -- (but) not this one," she said.
Again and again, critics in the US and, privately, diplomats from Europe and beyond raise the question of long-term damage to US credibility. Why would anyone feel comfortable working on a deal with one US administration, if the next one will simply ignore it, they ask.
"The United States has already destroyed a tremendous amount of its credibility by abandoning its international security partners," involved in the deal, said Elizabeth Rosenberg, director of the Energy, Economics and Security Program at the Center for a New American Security, and a former Obama administration official.
Administrations often inherit policies they dislike, but they generally work to amend them to retain continuity and credibility. "We didn't like Bush policies," said Ben Rhodes, President Barack Obama's deputy national security adviser, referring to President George W. Bush. "But we didn't go around with a wrecking ball to agreements made by other administrations. There has to be a degree of continuity."
Texas Rep. Joaquin Castro, a Democrat, wondered, "how does the President expect to marshal support for plans to address North Korea, Syria, or any other crisis after demonstrating his willingness to withdraw from an agreement led and negotiated by the United States?"
Iranian Twitter users were quick to make that point even as Trump made his midday address, hitting the social media service with the hashtag #NeverTrustUSA.
The most serious fallout of Friday's announcement could be a slide into greater instability and possible conflict, analysts and observers said.
Kremlin spokesman Dmitry Peskov, speaking to reporters in Russia, said a US pullout "will definitely harm the atmosphere of predictability, security, stability and nonproliferation throughout the world, which can seriously aggravate the situation surrounding the Iranian nuclear dossier."
"We already know Tehran's response," he said. "Tehran will also leave this agreement."
Legislation that the administration worked on with lawmakers would create "enhanced" restrictions on Iran's nuclear program, with triggers for additional sanctions.
"It places all these additional requirements on Iran that are not in the nuclear deal," Rosenberg said. "If Iran is in breach, it will re-impose nuclear sanctions. This is an effort by the President's party in Congress to up the ante on Iran and unilaterally try to change the terms."
In a statement to the press, the Iranian Mission to the United Nations said that if Iran's "rights and interests" are not respected, it will resume its nuclear program without any restrictions.
"The Islamic Republic of Iran will not be the first to withdraw from the deal, but if its rights and interests in the deal are not respected, it will stop implementing all its commitments and will resume its peaceful nuclear program without any restrictions" the statement read.
Majidyar said that would set off a chain reaction. "Ultimately it will lead to cancellation by the US or Iran," he said. And "if Iran resumes nuclear enrichment, 20 percent or more, that means the US or Israel have to take action," in response.
There's a good likelihood "that action would be military action," Majidyar said In the absence of a deal, a military strike on Iranian nuclear facilities wouldn't solve the long term problem of containing Tehran's nuclear program, he said. "You can damage nuclear sites physically, but you can't damage the know-how acquired over the last decade. They can reassemble."