As French President Emmanuel Macron visits Washington this week, he has been working to persuade President Trump to keep the United States participating in the nuclear agreement with Iran, but with expanded safeguards. Whether to stay in is a decision Trump has to make by May 12 — about a deal he has criticized since early in his campaign for president.

In January, Trump warned that he could withdraw the United States from the agreement unless Congress and the United States’ European partners addressed important concerns. Those included his worries that Iran’s missile program was still underway — and more important, that restrictions on Iran’s ability to enrich uranium would expire within 10 to 15 years.

Last year, then-Secretary of State Rex Tillerson noted that because of the agreement’s sunset dates, “one can almost set the countdown clock to when Iran can resume its nuclear weapons programs, its nuclear activities.”

But instead of canceling the agreement, the parties could extend it — so that Iran restricts enrichment for several years beyond the agreement’s sunset dates.

A brief refresher on the Iran nuclear deal

Iran has sought nuclear technology since well before its 1979 revolution. Iran’s Russian-built, light-water nuclear power plant at Bushehr is not controversial. However, the international community has worried about Iran’s centrifuges that enrich uranium. That is because while low-enriched uranium is used as fuel for reactors, high-enriched uranium can be used for nuclear weapons.

Iran clandestinely developed small-scale enrichment capabilities in the 1990s. By the 2010s, it had a substantial enrichment program, with about 20,000 centrifuges and 10,000 kilograms of low-enriched uranium — enough to make up to seven nuclear bombs. That is why, between 2002 and 2015, the United States and its Western European partners Britain, France and Germany, joined by Russia and China, pressured Iran through negotiations and sanctions to limit its enrichment program. These ended with the Joint Comprehensive Plan of Action, or JCPOA — known as “the Iran deal” — in July 2015, in which Iran agreed to limit enrichment and accept stronger monitoring in exchange for relief from sanctions.

Why did the deal have sunset provisions?

The deal restricts Iran to 5,000 first-generation centrifuges until 2025, and a stock of just 300 kilograms of low-enriched uranium until 2030. With these restrictions in place, it would take Iran about 12 months to enrich enough uranium for one nuclear weapon. Once these limits expire, Iran could operate many more centrifuges of a better quality, enabling it to enrich enough uranium for a bomb in weeks.

Tehran maintained — before, during and since the JCPOA was negotiated — that its goal wasn’t to build nuclear weapons but to enrich uranium for nuclear power plants. Iran doesn’t need to enrich its reactor fuel, because Russia provides fuel for Iran’s only power reactor, the one at Bushehr, and European nations have promised fuel for the smaller Tehran research reactor that produces medical isotopes.

What’s more, unless Russia gives Iran access to proprietary design information, Iran could not easily use its enriched-uranium to fuel the Bushehr reactor.

Still, Tehran insisted that it did not want to depend on Russia indefinitely for its nuclear fuel needs — and so it refused any nuclear deal that would forever prohibit it from enrichment.

Are renewal periods realistic? 

European diplomats have been discussing the possibility of extending the agreement. One option is asking Iran to extend the deal for periods of, say, 10 years, with the option of renewing for another 10 each time it expires.

Why would Iran agree? Two factors would be critical. First, suppliers must have delivered reactor fuel reliably in the past — reassuring Iran about its fuel supply. So far, that has been the case. Russia has consistently delivered fuel for the Bushehr reactor. Iran has signed contracts for two new Russian reactors, which Russia would fuel. What’s more, the International Atomic Energy Agency keeps an international fuel bank in Kazakhstan precisely to assure reserve supplies to its members.

Second, Tehran may want to be sure its regional rivals do not have enrichment and reprocessing programs. So far, that has been true. No Arab state has such technically challenging programs. The United Arab Emirates has renounced enrichment and reprocessing in a bilateral agreement with the United States, though Saudi Arabia has not. And as long as Tehran does not expand its enrichment program, its regional rivals have less reason to launch their own. That, at least, is the standard logic of arms control: Adversarial states mutually agree to limit their military-relevant technologies, assuring one another that there’s no need to develop such technologies.

Of course, geopolitics does not stay still. Iran may hesitate to renounce enrichment indefinitely, binding itself while the world around it changes. That’s why it may be more feasible to seek fixed, but still fairly lengthy, extension periods for the deal. This is the way some international agreements are negotiated, and for precisely the same reasons. The U.S.-Russia New-START treaty, which reduces strategic nuclear forces, was negotiated to last from 2011 to 2021, and can be extended for another five years. And the NPT itself, which entered into force in 1970, required an extension conference in 1995 “to decide whether the Treaty shall continue in force indefinitely, or shall be extended for an additional fixed period or periods.” The parties eventually opted for indefinitely extending the treaty in exchange for certain commitments from the nuclear weapons states.

What about Iran’s missiles?

Iran has hundreds of conventionally armed short-range missiles that can reach Arab states and medium-range missiles that can strike Israel. These missiles are less dangerous because of the JCPOA, which prevents Iran from quickly building nuclear warheads. Moreover, Iranian officials have stated that they would not build missiles with a range greater than 2,000 kilometers (1,243 miles). If Iran adheres to this commitment, it would not be able to strike Europe or the United States. And Iran’s space program can be restrained if it does not use solid-fuel rockets or if other states launch Iran’s satellites.

Would Iran agree? Tehran may be more likely to restrain its enrichment and missile programs for finite but renewable periods than indefinitely. That would still meaningfully restrain the nuclear and missile threat from Iran.

Dinshaw Mistry is a professor of political science at the University of Cincinnati and author of “Containing Missile Proliferation (University of Washington Press, 2003).