WASHINGTON (JTA) – U.S. President Donald Trump will present a major foreign policy speech this week on the Iran nuclear deal, reportedly decertifying its compliance with the 2015 agreement.

His words, ostensibly, will have consequences. Or perhaps not because of the type of decertification Trump reportedly is choosing. Or everything may change.

Here’s an explanation of what’s likely to happen on Thursday – and afterward.

What is Trump decertifying?

Trump is not decertifying Iranian compliance according to the deal per se, but according to a law passed by Congress in 2015, the Iran Nuclear Agreement Review Act, or INARA.

Trump has made no secret of his hatred of the agreement – the key foreign policy legacy of the predecessor Trump despises, Barack Obama. He has said the deal, which traded sanctions relief for a rollback of Iran’s nuclear program, was the worst he has ever seen.

Yet Trump has yet to exercise – and will not exercise on Thursday, according to reports – the clearest exit from the deal: reinstating the sanctions suspended by the pact. Under its terms, Trump can reinstate sanctions only if he establishes that Iran is not in compliance with the deal’s provisions, which restrict uranium and plutonium enrichment. UN inspectors have repeatedly confirmed Iranian compliance, most recently on Monday.

There’s nothing to stop Trump from reimposing sanctions even if Iran meets the narrow definitions of compliance; an inherent weakness of the agreement is that it is a political deal, not a treaty subject to international law. He can throw it out. Trump has said Iran is not in compliance with the “spirit” of the deal, suggesting that he has contemplated rupturing the agreement even absent evidence Iran is not in compliance. His top advisers, however, have counselled against an outright breach, arguing that it would isolate the United States from its allies.

The law, on the other hand, may give Trump an out in the form of a softer decertification: The president must not only certify every 90 days that “Iran is fully implementing the agreement,” but also that the suspension of sanctions against Iran is appropriate to Iran’s behaviour and “vital to U.S. national security interests.”

Advocates of taking a tougher stance on Iran are parsing that final clause: “and vital to U.S. national security interests.” They argue that the president may determine that the suspension of sanctions is no longer in the U.S. interest, even if Iran is technically in compliance with the nuclear deal. They cite Iran’s continued ballistic missile testing, its backing for terrorism and its military adventurism to argue that the funds that the sanctions relief has freed for Iran to use on its bad acts are not in the U.S. interest.

“The deal and the status quo are most certainly not in our ‘vital national security interests,’” Sen. Tom Cotton, R-Ark., a leading Senate advocate of decertification, said in a speech last week at the Council on Foreign Relations.

What happens next?

Leaders in both houses of the U.S. Congress may under the law introduce expedited legislation to reinstate sanctions as soon as the Oct. 15 deadline for certification passes. Congress then has 60 days to reinstate the sanctions under INARA.

Under the law, reinstatement unusually needs just a simple majority in the Senate – 51 votes in a body that has 52 Republicans. After the 60 days, Congress must amend INARA or enact new laws to reinstate sanctions. Under current rules, any such initiative will need to meet the Senate’s hard-to-breach 60-vote threshold to advance.

Does Congress get a new stab at it in another 90 days should Trump again decertify Iran? That’s not clear. Advocates for the deal say no, arguing that INARA gives Congress a single shot at reimposing sanctions with a simple majority. Deal skeptics say yes, the whole process moves back to “start” every 90 days.

The language of the law itself is obscure. Its tough oversight provisions were written in anticipation of Democratic presidents that a skeptical Congress feared would be eager to keep the deal in place. A Republican president, it was believed, would simply scrap the deal. Not anticipated was a Republican president who would punt the ball back to Congress.

Will Congress reinstate sanctions?

It’s not clear – it’s not even clear whether Trump wants Congress to reinstate the sanctions.

Mark Dubowitz, a longtime deal skeptic who helms the Foundation for the Defense of Democracies and has consulted with the White House on its decertification strategy, has counselled a “waive and slap” strategy: Trump should continue to waive sanctions under the deal while “slapping” Iran with sanctions unrelated to behaviour outside the purview of the deal, including its missile testing. Congress, he says, should not reimpose sanctions.

In a Wall Street Journal op-ed he wrote last month with David Albright, a former nuclear inspector, Dubowitz argued for decertification as a means of renegotiating aspects of what he sees as a flawed deal, particularly its clauses that remove some restrictions within a decade. But he emphasizes that Congress could scuttle that plan if it were to reintroduce sanctions.

“Reinstating the JCPOA sanctions after decertification would ruin the ‘decertify, waive, slap and fix’ approach,’” Dubowitz and Albright wrote, using the acronym for the deal’s formal name, the Joint Comprehensive Plan of Action. “To persuade Republicans, who are the most likely to vote to reinstate JCPOA sanctions that have been waived or lifted, the administration needs to demonstrate a comprehensive strategy to fix the deal and use all instruments of American power to neutralize and roll back Iranian aggression.”

Cotton, who also opposes the immediate reimposition of sanctions, says that decertification by Trump would function as a warning to Iran.

“Congress and the president, working together, should lay out how the deal must change and, if it doesn’t, the consequences Iran will face,” he said in his speech.

Yet Congress is a fickle creature, subject to the whims of 535 voices and pressures from outside its halls. There is no absolute guarantee that the 60 days will pass without sanctions reintroduced, and there are influential voices arguing for a reimposition of sanctions as well as for totally scrapping the deal.

John Bolton, the former ambassador to the United Nations whom Trump considered briefly for secretary of state, calls Dubowitz’s proposal “Jesuitical” in its nuances, “teasing out imagined benefits from adhering to a deal Iran already treats with contempt,” as he wrote this week in The Hill.

Congressional Republicans may also be wary of being set up by a president who is skilled at deflecting blame on others. Congress’ failure to reimpose sanctions could trigger a Trumpian tweet storm accusing lawmakers of weakness.

The weight of the evidence is nonetheless against Congress slapping on new sanctions. Under INARA, the reintroduction of sanctions must be approved by each chamber’s Foreign Affairs Committee. Rep. Ed Royce, R-Calif., the chairman of the House panel, has already said he prefers keeping the deal and “enforcing the hell out of it.”

Sen. Bob Corker, R-Tenn., Royce’s Senate counterpart, is currently feuding with Trump over what Corker has depicted as Trump’s foreign policy recklessness. He has not pronounced on what would happen should Trump trigger the review under INARA – a law Corker co-authored – but he may be loath to ratchet up tensions with Iran under an American president he has openly feared could trigger World War III.

What about the Democrats?

Democrats, including those who opposed the deal in 2015, unanimously oppose decertification and reimposing sanctions should Trump decertify. Among those arguing in recent days against decertification are leading Jewish lawmakers who opposed the original deal, including Sen. Ben Cardin, D-Md., the ranking Democrat on the Senate Foreign Relations Committee, and Reps. Eliot Engel, D-N.Y., Cardin’s counterpart on the House committee, and Ted. Deutch, D-Fla., the top Democrat on the House Middle East subcommittee.

Their argument is that decertification absent any evidence that Iran is violating the deal would render a blow to America’s reputation as a reliable partner to the countries who joined the United States under Obama in negotiating the deal.

“If the United States wants to prevent Iran from rushing to a bomb and fomenting further instability in the region, then we must work with our allies to build support for a shared agenda,” Engel wrote Tuesday in USA Today. “If we walk away from the nuclear deal, we lose our leverage.”

Cardin has called on Trump to use existing non-nuclear-related sanctions to pressure Iran, including a package passed earlier this year overwhelmingly by Congress.

“In addition to vigorously enforcing the Iran agreement, the president should immediately follow the law by implementing these sanctions, working with our European allies, rather than sending the United States down a path that undermines our ability to continue pressure through sanctions on Iran, North Korea, and Russia; weakens the trans-Atlantic alliance; and damages U.S. leadership and credibility,” he said last week.

Where’s AIPAC?

The American Israel Public Affairs Committee (AIPAC) has yet to specifically address decertification, although it remains committed to addressing what it sees as flaws in the deal.

That may change: AIPAC’s National Council rolls into Washington over the weekend, a couple of days after the Trump speech. On the agenda for its activists are meetings in congressional offices, and Iran is one of several topics of discussion. Should Trump’s speech provide guidance amenable to AIPAC, the lobby may endorse his strategy.

However, a key element of AIPAC lobbying has always been bipartisanship. Whether or not it decides to back fresh sanctions, AIPAC would need the backing of prominent Democrats.

J Street, meantime, the liberal pro-Israel lobby that played a key role in backing the deal, is pushing its activists to remind lawmakers that they are opposed to decertification.

So no reimposition of sanctions, no effect?

Not quite. American allies – including governments friendly to Trump, like Britain and France – have emphatically said they would be frustrated by decertification. Last week, Britain’s embassy posted a graphic on Twitter purporting to show how the Iran deal has been effective.

Decertification could further isolate the United States.

“The Trump stock is not very high in European and other capitals these days,” David Harris, who heads the American Jewish Committee, wrote Tuesday on the Huffington Post, noting his group’s longstanding skepticism of the deal. “That being the case, will any new moves by Washington be seen as nothing more than saber-rattling and brinkmanship, without a convincing and constructive plan behind it?”

What about Iran?

Javad Zarif, Iran’s foreign minister, told Politico earlier this month that decertification would mean little should Congress not reimpose sanctions. But that posture could change.

Business with pariah states suffers not just when sanctions are imposed, but when they are threatened or even contemplated. Iran’s markets, still rebuilding with the removal of some sanctions, could suffer a blow merely from Trump’s speech. That would strengthen hardliners in Iran who want out of the deal.