Updated on October 13, 2017

On Friday, the Trump administration announced that it will not certify the nuclear deal that Barack Obama’s government struck with Iran and other world powers.

Critics claim the decision could isolate the United States from its allies, set Iran sprinting toward nuclear weapons, and increase the likelihood of military conflict. Supporters argue that the move is the best way to block Iran from acquiring nuclear weapons. Skeptics dismiss the act as mere political posturing—a way for Trump to appear to honor his campaign promises while kicking the can to Congress and ultimately sticking with the agreement.

In explaining his decision, however, Trump didn’t sound like a man engaged in symbolic acts. “We will not continue down a path whose predictable conclusion is more violence, more terror, and the very real threat of Iran’s nuclear breakout,” he said in a speech at the White House. “In the event we are not able to reach a solution working with Congress and our allies, then the agreement will be terminated. It is under continuous review, and our participation can be canceled by me, as president, at any time.”

So what actually happens next? Here’s a primer.

What Certification Means

In 2015, around the time that the Obama administration was finalizing an international agreement to restrict Iran’s advancing nuclear program, Senators Bob Corker and Ben Cardin helped pass bipartisan legislation requiring the president to certify certain things about the deal to Congress every 90 days. The bill was basically a way for skeptical lawmakers to assert some control over an accord that Obama hadn’t negotiated as a treaty, which would have required Senate approval.

Trump, who regularly denounces the nuclear deal and views Iran as one of America’s fiercest enemies, twice heeded the advice of his foreign-policy advisers and grudgingly certified the agreement. But this third time, when the certification deadline coincided with the conclusion of a broader administration review of its Iran policies, he opted not to. Critically, he hasn’t done so on the grounds that Iran is violating the terms of the agreement, which deals narrowly with Iran’s nuclear program. Trump’s own government, United Nations inspectors, and the other parties to the deal all agree that the Iranians haven’t substantively breached the accord and that the Iranian nuclear program has been mothballed for the time being.

Instead, Trump is citing a provision of the Corker-Cardin law, officially known as the Iran Nuclear Agreement Review Act (INARA), which asks whether the lifting of sanctions imposed in retaliation for Iran’s nuclear program is in America’s national-security interests and “appropriate and proportionate” relative to Iranian measures to draw down the nuclear program. The Trump administration is essentially saying it’s not—because of flaws in the Iran deal, because Iran has continued testing ballistic missiles that could theoretically carry nuclear weapons, and because Iran has persisted with aggressive policies that the United States abhors, including propping up Bashar al-Assad’s government in Syria and supporting groups such as Hamas and Hezbollah that the U.S. considers terrorist organizations.

It’s worth emphasizing, however, that declining to certify the stipulations of INARA is a procedural move under U.S. law with no direct or immediate impact on the international nuclear deal with Iran. It’s not synonymous with ripping up the agreement. It would not make the United States non-compliant with the accord. What it does is punt the Iran debate to Congress, where the ramifications of decertification could prove much greater.

Of the scenarios below, #1 is the most consequential, #2 is currently the Trump administration’s preferred outcome, and #3 is a distinct possibility.

shutterstock / The Atlantic

Scenario #1: Congress Ends the Iran Deal

Now that Trump has declined to certify, the minority or majority leaders in either house of Congress have 60 days to introduce legislation to reimpose nuclear-related sanctions on Iran. These include the severe measures against the country’s banking system and oil exports that helped force the Iranians into negotiations during the Obama administration. If such a sanctions package were to get through Congress, there’s little chance Trump, who set the whole process in motion, would veto it.

Reinstating these sanctions would put the United States in breach of the Iran deal and could lead to the unraveling of the agreement in a matter of months. Iranian Foreign Minister Javad Zarif has said that Iran could choose to remain in the deal even without the United States. This would depend on whether Britain, France, and Germany, who are also signatories to the accord, decide to join in the renewed punishment of Iran or to resist it—and each of these countries has expressed support for keeping the deal. (China and Russia, the other parties to the deal, are much less likely to take America’s side in any dispute over the future of the Iran deal.)

How Europe would respond to the United States reimposing nuclear sanctions is a live question. David O’Sullivan, the European Union’s ambassador to the United States, recently suggested that the EU might try to legally shield European companies doing business with Iran from having to comply with American sanctions, but acknowledged some uncertainty in an interview with my colleague Krishnadev Calamur. “I don’t think anyone, frankly, has thought through what they would do if one of [the Iran nuclear agreement’s] signatories said they consider themselves no longer bound by the deal,” O’Sullivan told him. Joe Kaeser, the CEO of the German conglomerate Siemens, which struck several infrastructure deals with Iran following the lifting of sanctions last year, seemed more resigned when I spoke with him this month. “If the world believes that Iran doesn’t play by the rules and imposes sanctions, then we’ll follow them whether we have an opinion about it or not,” he said.

Many former Obama administration officials believe the Iranians would stop complying with the deal and ramp up their nuclear program if the United States were to reverse course on sanctions relief. Philip Gordon, Obama’s top Middle East adviser, envisions Iran removing caps on stockpiles of enriched uranium that could be turned into weapons-grade nuclear material, reinstalling centrifuges to enrich that uranium, and reconstituting a heavy-water reactor that could produce weapons-grade plutonium.

“We would be right back to where we were in the first place when we agreed to this deal, which is to say Iran step by step getting to the point where they’re on the verge of a [nuclear] weapons capability,” Gordon has said. “The choice for the United States becomes clear and binary, which is to say: Accept that they develop a nuclear capability or bomb them to prevent them from having it.”

In a speech earlier this month at the Center for American Progress, the Democratic Senator Chris Murphy forecast additional fallout from the United States ditching the Iran deal by reimposing sanctions, arguing that it would further fray U.S.-European relations and dash hopes, however remote at the moment, of a diplomatic resolution to the standoff over North Korea’s rapidly developing nuclear-weapons arsenal.

“If the U.S. pulls the plug, despite Iran’s compliance, just because we’re idiots,” it will “shred our credibility and isolate the United States from our partners and allies just at the moment when the North Korean crisis commands us to be rallying the globe to meet this new threat,” Murphy said. “Why would [Kim Jong Un] have any reason to believe that we would uphold our end of the bargain?” The upshot: A devastating war on the Korean peninsula would grow more likely.

The Republican Senator Tom Cotton, who has been closely consulting with the Trump administration on its Iran strategy, claims that Iran’s withdrawal from the nuclear deal could be managed, even if that requires initiating another bout of instability and military conflict in the Middle East. The Trump administration could respond by imposing a trade and financial embargo on Iran that “will likely create economic chaos and destabilize the regime” within the estimated 12-month timeframe it would need to build nuclear weapons, he argued during a recent address at the Council on Foreign Relations. And if not, the economic pressure would at least “buy time” for the United States to launch “calibrated strikes” against Iran’s nuclear infrastructure. “If they choose to rebuild it, we could destroy it again, until they get the picture,” Cotton vowed.

Scenario #2: Congress Seeks to Improve the Iran Deal

There is good reason to believe that congressional leaders will refrain from immediately reimposing nuclear sanctions on Iran, which Secretary of State Rex Tillerson, in a briefing with reporters on Thursday, acknowledged would be “tantamount to walking out” of the deal.

The president himself isn’t calling for Congress to reinstate these sanctions. Trump, in fact, has the authority to withdraw the United States from the nuclear agreement without any help from Congress. He could have declined to waive nuclear sanctions against Iran, which are technically still in force absent the waivers, when they came up for review in September. But he didn’t. And even if Trump were to change his mind in the coming days and urge the Republican-controlled Congress to snap back sanctions, it’s unclear that he would have the votes. Several GOP senators, including Rand Paul and Susan Collins, have expressed reservations about quitting the nuclear deal (then there’s Bob Corker, who despite being an architect of INARA is now Trump’s newly minted nemesis).

What Trump wants Congress to consider, according to Tillerson, is amending the INARA legislation so that it includes specific “trigger points” related to unacceptable Iranian nuclear- and missile-related activities. If Iran were to carry out any of these activities, it would automatically trigger the reimposition of nuclear sanctions—and thus U.S. withdrawal from the accord—without any congressional action or debate. Since the legislation would cover Iran’s missile program and wouldn’t have an expiration date, the administration believes the law would plug two holes in the current agreement: the fact that certain restrictions on Iranian nuclear activities lapse after 10 or 15 years, and the lack of limits on Iran’s development of missiles.

These amendments would “outlive” the nuclear deal, Tillerson said, and demonstrate that the U.S. government is “never going to accept [the Iranians] resuming their nuclear-weapons program.” Tillerson added that the administration has shared with Congress—presumably at least with Corker and Cotton, who are expected to introduce the legislation—a “notional draft” of what these trigger points could look like, though he didn’t go into more detail. (Reports suggest that the 90-day reporting requirement in INARA could also be adjusted so that Trump doesn’t have to go through the political ordeal of certifying a deal he hates four times a year.)

If Congress modifies the INARA law, the Trump administration would then use the legislative statement to pressure the Iran deal’s other signatories to either renegotiate the Obama-era agreement—a result Tillerson admitted was “unlikely”—or negotiate a supplementary agreement that addresses America’s concerns about Iran’s missile program and ability to restart its nuclear program within a decade or so.

The Trump administration will simultaneously ratchet up the heat on Iran by slapping it with an array of non-nuclear sanctions—against the country’s Islamic Revolutionary Guard Corps, for instance—that wouldn’t violate the nuclear agreement. And it will urge its European allies to do the same.

One fundamental problem with this plan, as the former Obama administration official Colin Kahl has put it, is that a “better deal” may well be a myth. As he notes, referring to the nuclear deal by its formal name, the Joint Comprehensive Plan of Action, or JCPOA:

Although European leaders have suggested that they are open to considering “supplemental” arrangements to address issues not covered by the nuclear accord, they are adamantly opposed to renegotiating the JCPOA itself. China and Russia are even more skeptical of doing so. …

Thus, even if Trump’s gambit to decertify and threaten the JCPOA did some harm to Iran, the international reaction would produce far less net economic and diplomatic pressure on Iran than existed before the JCPOA was finalized. And it is literally insane to believe that it is possible to produce 150 percent of the current deal with 50, 70, or even 99 percent of the leverage the United States possessed in 2015. It simply ignores the laws of diplomatic physics. …

Any realistic prospect of extending the life of the JCPOA’s nuclear constraints … will require a “more for more” approach that puts positive incentives—such as providing Iran with access to the U.S. financial system to conduct dollar transactions or completely lifting the U.S. primary embargo—on the table, not just additional sanctions and threats.

If a better deal does indeed prove elusive—if Corker and Cotton can’t muster enough votes to amend INARA to Trump’s liking, if the Europeans and Russians and Chinese refuse to renegotiate, if the Iranians reject harsher terms without corresponding concessions, if Tillerson’s vacancy-plagued State Department can’t pull off this towering diplomatic feat—that could return Trump and his partners in Congress to Scenario #1. The president could, as he warned on Friday, bypass Congress entirely and quit the deal on his own. Even assuming that Trump’s tougher stance on Iran gets codified into law, the nuclear agreement could collapse if the new legislation alienates the other parties to the accord or Iran tests a “trigger point.”

“They decertify so as to destabilize, and then they have the tools to at any moment—in a month, in a year, in two years—say, ‘OK now we’re done [with the nuclear deal]. And by the way we had some help from Congress in authorizing our right to do that,’” Jake Sullivan, a top State Department official in the Obama administration, has argued.

Scenario #3: Congress Does Nothing

Trump’s move to decertify could end up the way his push for health-care reform did—with a whole lot of posturing and debate and false starts in Congress, and little to show for it. It could amount to Trump head-faking to a campaign promise and making a political statement about the folly of his predecessor without actually undoing that predecessor’s policy. “I don’t want to suggest to you this is a slam dunk up there on the Hill,” Tillerson conceded. “We know it’s not.”

(The gambit could also backfire in the opposite direction—by blowing up the Iran deal even if that’s not what Trump wants. The elaborate decertification plan “suggests an elegance of plotting that the administration has given little evidence of possessing,” Kori Schake writes in The Atlantic. “Congress is unlikely to trust the president enough to make a brave choice—which remaining in the agreement after the president decertifies it would be—they suspect he would then publicly castigate them for.” Once you toss the Iran deal to 292 Republicans, many of whom opposed Obama’s negotiations with Iran and have been burned by Trump in the past, you simply don’t know what will happen.)

But if decertification ends in a whimper, it’s a very risky step to take for that payoff. The decision not to certify will lead to a prolonged period of uncertainty among America’s allies. It could make European banks and companies more reluctant to do business with Iran, which could harm the Iranian economy and increase opposition to the deal among Iranians. It alone could send a signal, as Murphy warned, “that American presidents cannot be trusted to uphold deals done by prior presidents.” All this might not kill off the Iran deal at once. But it could, as Sullivan put it, spark a series of tit-for-tat provocations by the Iranians and Americans—an inglorious death of the agreement “by a thousand cuts.”