Here are the four main options available to them, listed in order of most to least damaging to the deal itself. It's not clear which option Congress will choose.
1. Impose sanctions on Iran: Either new or old ones. This would be the most aggressive thing Congress could do. It would effectively end the United States' involvement in the deal and potentially end the global deal itself, as the whole reason for Iran to come to the negotiating table is to be able to do business with countries that had closed it off. Iranian President Hassan Rouhani has warned that Iran could end its side of the deal “within hours” if Congress imposes new sanctions.
Who's advocating this: Hardly anyone. Yet.
Is it likely? No. Trump has called the Iran deal “one of the worst deals I've ever seen,” but if he wanted to tear it up, he would have either decertified it earlier this year when he had the opportunity or tried to issue new sanctions. He hasn't done either, and the The Washington Post's Anne Gearan and Karoun Demirjian report that he doesn't plan to recommend that Congress tear up the deal by imposing sanctions either.
Even some of the Iran deal's most vocal opponents want to try No. 2 first.
2. Try to get other countries to renegotiate the deal: Congress could send a message to the rest of the world that it wants to change the deal. It could do this by voting on a resolution that says the United States wants to extend restrictions on Iran's nuclear plan indefinitely instead of ending it in a decade. Or it could require Iran to stop testing ballistic missiles if it wants to keep the deal. (This summer, Congress passed a bill that sanctions Iran for testing ballistic missiles.) Supporters of this proposal argue that under the current deal, Iran's path to a nuclear bomb is just delayed.
Who's advocating this: Sen. Tom Cotton (R-Ark.), one of the Iran deal's most vocal opponents, has called this option “coercive diplomacy.” If it doesn't work, he wants Congress to revisit tearing up the deal by imposing sanctions.
“The world needs to know we’re serious, we’re willing to walk away, and we’re willing to reimpose sanctions,” he told the Council on Foreign Relations last week.
Is it likely? Cotton is optimistic, but at least one international expert isn't. The European Union and the United Nations have said the deal is working, so why would they join the United States to renegotiate it, said Anthony Cordesman, a military strategy consultant with the Center for Strategic and International Studies. “Who on Earth is going to be persuaded? What are you going to do? Threaten to beat them to death in the alley if they don't join us?”
Some of Trump's top advisers, including Defense Secretary Jim Mattis, think Iran is cooperating, too.
3. Hold hearings that tsk tsk Iran: Consider this a subtler way for Congress to urge the international community to renegotiate the deal. The aim would be to press Iran to get in line and world powers to force Iran into a tougher deal. “Hearings are weapons,” Cordesman said.
Who's advocating this: Sen. Bob Corker (R-Tenn.), chairman of the Senate Foreign Relations Committee, isn't ruling it out. “I think that we may well have some legislative opportunities coming up soon relative to Iran,” he told reporters last week.
Is it likely? Yes. Before Congress considers any legislative options, it probably will hold hearings. And Republicans could put together hearings that showcase experts who think Iran isn't holding up its end of the bargain.
4. Do nothing: Trump decertifying the deal would be mostly symbolic. It would signal to the international community that he doesn't think the deal is in the national security interests of the United States. But it would not actually pull the United States out of the deal. That's up to Congress. Congress could fail to act, and the deal would stay in place.
Who's advocating this: Democrats. They largely want to keep the deal intact, in part because they think tearing it up with sanctions would undermine U.S. credibility with the rest of the world. “Leaving the [deal] at this point, absent concrete facts and material determinations, would isolate us from our allies and partners,” Sen. Benjamin L. Cardin (Md.), the ranking Democrat on the Senate Foreign Relations Committee, said in a statement.
Is it likely? Yes. Republicans control a majority in both chambers, but in the Senate, Democrats could filibuster any legislation changing the Iran deal.