JUDY WOODRUFF: Another hallmark of the Obama administration is the Iran nuclear deal.
And a deadline looms this weekend to certify whether Tehran is in compliance and whether the agreement is in the U.S. national security interest.
There is fierce debate over what President Trump should do.
But we wanted to step back to look at what the deal does and what it does not do, and what the president's decision could mean.
Nick Schifrin is here to put it in context.
NICK SCHIFRIN: In 2015, the United States and a united world community made a deal with Iran. Iran severely restricted its nuclear program, allowed more access to international inspectors, and promised never to seek, develop, or acquire any nuclear weapons.
Before the deal, U.S. and Israeli intelligence believed the breakout time for Iran to build a nuclear weapon was as little as one month. After the deal, the breakout time is at least 12 months.
In return, the U.S. and the U.N. lifted sanctions related to Iran's nuclear program worth more than $100 billion, and promised not to discourage investment in Iran. The deal was announced by the European Union's top diplomat, Federica Mogherini.
FEDERICA MOGHERINI, Foreign Policy Chief, European Union: We delivered on what the world was hoping for, a shared commitment to peace and to join hands in order to make our world safer.
NICK SCHIFRIN: The deal's critics were unconvinced.
PRESIDENT DONALD TRUMP: I know deal-making. And let me tell you, this deal is catastrophic, for America, for Israel, and for the whole of the Middle East.
NICK SCHIFRIN: The first criticism is the deal's expiry dates, or so-called sunsets.
After eight years, Iran can begin to slowly manufacture increasingly advanced centrifuges to enrich uranium. After 15 years, Iran can start producing higher-grade uranium, and can expand its stockpile of uranium. And after 20 years, Iran can restrict international monitoring.
The deal's advocates counter that all arms deal have sunsets, and that the deal has important permanent restrictions. Iran is forever banned from activities that could contribute to the development of a nuclear explosive device, and is forever required to notify inspectors if it's building a nuclear facility.
The critics also condemn what's not in the deal. Iran helps arm militant groups in the Middle East, including Hezbollah, deemed a terrorist group. The deal doesn't prevent that. Iran launches and trades ballistic missiles. The deal doesn't prevent that. And Iran helps the Syrian regime's brutal crackdown. The deal doesn't prevent that either.
The deal's defenders say it was never designed to confront those other issues, and it's better to do that confrontation when Iran doesn't have an active nuclear program.
But the deal does say world powers expect Iran to positively contribute to regional and international peace and security. And critics argue Iran, even if it's in technical compliance, is going against that, against the so-called spirit of the deal.
PRESIDENT DONALD TRUMP: We cannot abide by an agreement if it provides cover for the eventual construction of a nuclear program.
NICK SCHIFRIN: So, what's next?
Administration and congressional officials tell me they expect the president will not certify Iran is in compliance with the deal, based on national security grounds. That will trigger a 60-day window, during which Congress can go vote for against snapping back sanctions, meaning reimposing nuclear-related sanctions on Iran.
That would likely kill the deal. But even the deal's most strident critics, such as Senator Tom Cotton, say Congress shouldn't kill the deal. They want the 60-day window, so the U.S. can gain leverage to get Iran to change the deal, even if that takes many months.
SEN. TOM COTTON, R-Ark.: The world needs to know we're serious, we're willing to walk away, and we're willing to reimpose sanctions, and a lot more than that.
NICK SCHIFRIN: The Trump administration wants to change all Iranian behavior. But it's not clear it's possible to do so by renegotiating the nuclear deal.
Iran says it won't renegotiate. And with the possible exception of France, none of the other countries who signed the deal want to renegotiate.
Wendy Sherman led the Obama team that negotiated the deal.
WENDY SHERMAN, Former Undersecretary of State for Political Affairs: If the president doesn't certify, even if Congress doesn't snap back sanctions, which is this Kabuki smackdown, their ability to pull off this Kabuki dance is in great question. As a result, we will isolate ourselves from the rest of the world.
NICK SCHIFRIN: The next few months will be dominated by uncertainty, uncertainty what Congress will do, and uncertainty how Iran will respond to Washington's decisions. The deadline for the president to announce his decision is Sunday.
For the PBS NewsHour, I'm Nick Schifrin.