This week, President Trump will again have an opportunity to gut the Iran nuclear deal — or not.

By Friday, Trump must decide whether he will maintain the relief from economic sanctions offered to Iran's central bank under the deal. If he declines to do so, it would result in the reinstatement of major sanctions on the country. That would be a big blow to the deal.

According to the Associated Press, he is leaning toward extending sanctions relief, though he is considering new, targeted sanctions on Iranian businesses and people. (For some Iranian companies, that may effectively erase the gains of the 2015 deal.)

U.S. allies have been pressuring Trump to stay the course on the deal. Representatives from the European Union, Britain, France and Germany met with the Iranian foreign minister this week. Afterward, they emphasized their continued support for the accord, stressing that Iran was in full compliance with its terms.

“The deal is working. It is delivering on its main goal, which means keeping the Iranian nuclear program in check and under close surveillance,” E.U. foreign policy chief Federica Mogherini said, according to the BBC.

“I don't think that anybody has produced a better alternative to the JCPOA as a way of preventing the Iranians from going ahead with the acquisition of a military nuclear capability,” British Foreign Secretary Boris Johnson said after the meeting, referring to the nuclear deal by the abbreviation of its formal title — the Joint Comprehensive Plan of Action. “It is incumbent on those who oppose the JCPOA to come up with that better solution, because we have not seen it so far.”

Trump is a longtime opponent of the deal, which he has called the worst in history. In October, he officially disavowed the deal. But he stopped short of terminating it, instead punting the issue to Congress. He wants to ditch the deal's “sunset clauses,” which lift restrictions on Iran's uranium-enrichment program and other sensitive activities 10 to 15 years after implementation of the accord, which occurred in January 2016. (Highly enriched uranium can be used to create nuclear weapons. However, Iran has not enriched uranium to weapons grade, according to the U.N. nuclear watchdog agency.)

Why does Trump want to ditch the Iran deal?

By all accounts, Iran has complied with the terms of the deal. U.S. officials have said so; European allies have agreed. The United Nations watchdog tasked with monitoring compliance has visited Iran several times and certified that the country is limiting its nuclear activities, per the terms of the deal. Last week, the U.S. defense secretary and the chairman of the Joint Chiefs of Staff expressed qualified support for the deal before Congress.

But the president and his administration say Iran is not following the spirit of the accord, which they see as de facto noncompliance. Secretary of State Rex Tillerson and others have said that Iran has not positively contributed to regional and international peace and security, an “expectation” embedded in the deal's preamble. They noted that Iran still supports militant groups such as Hezbollah and Hamas and backs militias in Syria and Yemen. Iran has also continued to test ballistic missiles, something that irks the United States, even though such tests do not constitute a violation of the agreement.

In October, Trump “decertified” the deal. What does that actually mean?

The U.S. president is required by Congress to certify every 90 days that Iran is complying with the deal. Trump did so twice. Then, in October, Trump decertified the deal, arguing that it was not in the United States' national security interest.

On its own, that doesn't mean much. If the United States does not impose new nuclear-related sanctions, it is not technically in violation of its obligations under the agreement.

So far, Trump has seemed leery of doing that on his own. Instead, he has pushed Congress to come up with “new legislation codifying Trump’s conditions for remaining in the ... Joint Comprehensive Plan of Action.” As a Republican aide explained, “To get us on the right foot on the Iran strategy, we do need to use this certification decision, this moment, to launch a real effort to plug the holes and the weaknesses in the JCPOA.”

Could Congress decide to reimpose sanctions?

If Trump decertifies the deal, Congress will have 60 days to decide whether to reimpose sanctions on Iran, the ones that were suspended in exchange for that country's curbs on its nuclear program.*

That seems pretty unlikely. Congress would need only 51 votes to impose those sanctions. But it doesn't seem as if Republicans have the support they need to push something through. As The Post reports, Senate Majority Leader Mitch McConnell (R-Ky.) does not want to add another contentious issue to the legislative calendar, especially not with midterm elections approaching. Republican Sens. Jeff Flake (Ariz.), John McCain (Ariz.) and Susan Collins (Maine) have also said they're not sure how they would vote on sanctions. Sen. Rand Paul (R-Ky.) and House Foreign Affairs Committee Chairman Edward R. Royce (R-Calif.) say they don't think Trump should retreat from the deal. And Democrats seem universally opposed to new sanctions.

Given that, it's hard to imagine Republicans mustering the votes they need to impose any serious sanctions.

So, then, what is the president trying to accomplish? 

Even many proponents of decertification don't think the United States needs to reimpose sanctions. They reckon that the Trump administration can use the process as a way of persuading European allies to join the United States in advocating for a stronger Iran deal. In a speech at the Council on Foreign Relations last week, Sen. Tom Cotton (R-Ark.) laid out what that might look like. He has called for a bill that would eliminate the “sunset clauses” that lift restrictions on some Iranian nuclear activities after 10 or 15 years. He also would like to see tougher inspections and new curbs on Iran's ballistic and cruise missile programs.

What's Europe's position? 

If the United States backs out of the deal, it will almost certainly do so alone.

The other parties involved in the deal and the U.N. watchdog tasked with monitoring compliance say things are working. “We will not follow the United States in reneging on our international obligations with this deal,” a European Union official told The Post on Thursday. Russian Foreign Minister Sergei Lavrov told reporters, “It is very important to preserve it in its current form, and, of course, the participation of the United States will be a very significant factor in this regard.”

It's not totally clear how the international community will respond to Trump. But one thing is all but certain: If the administration backs out of the deal, it would isolate the United States from its allies and weaken its stature abroad. As my colleagues reported:

More than any other issue that has threatened transatlantic cohesion this year, President Trump’s decision to decertify Iranian compliance with the nuclear deal could start a chain of events that would sharply divide the United States from its closest traditional allies in the world. “After the Paris climate decision,” in which Trump withdrew the United States from a widely supported, painfully negotiated accord, “this could push multilateralism to the breaking point,” said a senior official from one of the three European signatories to the Iran deal.

How will the business community respond?

Since the deal was signed in 2015, several big companies have begun to do business in Iran. New sanctions by the United States would make things significantly more difficult. As Vox explained:

New sanctions would also force American allies to choose between doing business with Iran or with the U.S. Iran has begun to reintegrate itself into the global economy in the past year, and it has developed meaningful business ties with big companies that are based in the countries that struck the Iran deal. For example, this summer Iran signed a $5 billion agreement with France’s Total SA and China’s state-run China National Petroleum Corporation to develop its South Pars natural gas field.

Already, the European Union has begun taking steps to protect its businesses from U.S. retaliation. Officials are looking at measures used in the 1990s to shield companies and individuals from secondary U.S. sanctions. “I've no doubt that if this scenario materializes, the European Union will act to protect the legitimate interests of our companies,” David O’Sullivan, the E.U. ambassador to the United States, said at a September meeting.

U.S. sanctions may even make it easier for European companies to compete in Iran. “U.S. decertification would not necessarily end the deal — the U.S. just wouldn't be part of it anymore,” Robert Litwak, a member of the National Security Council under President Bill Clinton and an expert on international security at the Woodrow Wilson Center, told CNBC. “The Europeans won't return to sanctions so quickly. If this enables Airbus to beat out Boeing, they'd be delighted.”

How might Iran respond?

Iranian President Hassan Rouhani has said that he will not reopen negotiations, and Iran's top nuclear official said Monday that his country might rethink its cooperation with the International Atomic Energy Agency if the United States withdraws from the deal.

But Iran may stay in the agreement as long as the other signatories stick to the deal.

As CNBC put it:

If the U.S. decertifies the deal, “the ball immediately goes to Iran's court,” said Michael O'Hanlon, a foreign policy expert at the Brookings Institution. Iran “could have their cake and eat it too.”

It would be possible, O'Hanlon explained, for Iran to keep the benefits it gets from the agreement — namely, to continue to legally export oil. Then, a few years down the road it could argue that the agreement is null due to a lack of compliance from the United States. It could then resume nuclear activities.

That's not an attractive prospect for U.S. decision-makers, because it would force them to make a choice: either attack Iran's nuclear facilities, or push for new sanctions from a group of countries that will almost certainly be reluctant to give up business ties with Iran.

* Correction: An earlier version of this article incorrectly stated that Iran had a nuclear weapons program. It has a nuclear power program. Iran has not developed or acquired a nuclear weapon.