President Trump said Friday that he would not certify the 2015 Iran nuclear deal that is a legacy of his predecessor, and he asked Congress to figure out ways to address his concerns or he would end it himself. Trump's decision keeps the nuclear deal intact for now but maybe not for long.

Q. Why doesn't decertification blow up the deal?

A. Nothing in the nuclear deal requires certification, and none of the six other countries that signed it require their heads of state to do so, as U.S. law does. When Congress passed the Iran Nuclear Agreement Review Act (INARA) in 2015, the idea was that the president would notify Congress if Iran was cheating so Congress would have a brief, 60-day window to "snap back" U.S. sanctions.

Certification wasn't envisioned as a tool for a president to undermine the deal or use it as a way to reopen negotiations. But the INARA isn't just about whether Iran is meeting its obligations. It requires the president to determine whether the suspended sanctions are "appropriate and proportionate" and in the U.S. national interest. That Trump was not prepared to do. Still, decertification is not the same as walking away from the deal, at least not for the time being. It just transfers the decision to Congress.

Q. What will Congress do?

A. It has several options. The most extreme would be to reimpose U.S. sanctions that were lifted as part of the agreement, officially known as the Joint Comprehensive Plan of Action. But that would immediately place the United States in violation of the deal, and Trump is not asking Congress to do that. Instead, he's asking lawmakers to amend the INARA to impose new U.S. requirements on Iran. However, Iran would view that as a one-sided renegotiation of the agreement's terms and is unlikely to accept it. So it would fall to a joint commission of the seven signatories to determine whether the United States was violating the deal.

If Iran decided to resume its nuclear program in response, the United Nations Security Council would get involved to decide whether to put U.N. sanctions back in force.

Another option for Congress is simply to change the timetable so the president doesn't need to certify Iran's compliance every 90 days, as is now required. That could be more palatable to Trump, who certified Iran twice before, in effect admitting that the deal he lambasted on the campaign trail is working.

Q. So is the Iran deal safe?

A. Far from it. The administration wants Congress to set new conditions that address Iran's support for militias in Lebanon, Syria and Yemen, and to rein in Iran's ballistic-missile testing. It also wants Congress to make it clear that the United States will snap back sanctions at various "trigger points," such as if Iran resumes nuclear activities after the various "sunset" provisions expire years in the future. Merely passing the provisions may not alter the deal until sanctions are actually imposed. But Iran probably would argue that the United States is indeed changing the deal's terms by promising sanctions for activity that the deal permits. In any case, the deal may be doomed long before the deadline nears for a single sunset provision. Trump said that if his concerns aren't addressed by Congress and European allies that were partners in the deal, "then the agreement will be terminated."

Q. Is the administration applying any pressure on Iran to get it to bend?

A. Shortly after Trump began speaking Friday, the Treasury Department slapped sanctions on the Islamic Revolutionary Guard Corps, an independent arm of the Iranian military that sends fighters into neighboring countries, conducts missile tests and is heavily involved in the Iranian economy, including smuggling black-market goods. But the IRGC is already heavily sanctioned. And the Treasury sanctions were part of an executive order, not a more-onerous State Department designation. It telegraphs the administration's get-tough attitude.

Q. What will Iran do?

A. Iran has a lot to gain by doing nothing, particularly if Europeans stick to the deal and keep conducting business with Iran. To much of the world, the United States is the country that may end up reneging on its commitments, not Iran. That gives it a claim to hold the high ground, and it could just stand by watching while a wedge is driven between the United States and Europe.

Federica Mogherini, foreign policy chief of the European Union, said after Trump's speech that the nuclear deal is working and that the United States does not have the right to unilaterally change it. If Congress tries to reimpose sanctions, Europeans already are considering ways to protect their businesses that want to keep investing in Iran.