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.

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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.