President Donald Trump dumped the fate of the Iran nuclear deal on US lawmakers Friday, leaving open the question of whether they can turn the screw on Tehran without killing the accord.
Unveiling an aggressive new strategy against what he called the "rogue regime" in Iran, Trump said he will not certify under US law that the 2015 pact remains in the US interests.
He threatened that he could as president cancel the deal "at any time" but, rather than doing so, he left it up to Congress to decide whether to levy new US sanctions on Iran that might capsize the agreement.
Two influential Republican senators have drawn up a plan for sanctions that European diplomats fear would amount to a repudiation of the 2015 international accord, but it is unclear whether they could muster a majority.
There is broader support for fresh pressure on Iran over its continued missile development and subversive activities in the region -- factors that Trump says violate the "spirit" of the agreement.
But can Democrats and Republicans agree on measures that would stop short of destroying an accord that was the product of many years of diplomacy and is fiercely defended by US allies in Europe and fellow members of the UN Security Council.
"I am directing my administration to work closely with Congress and our allies to address the deal's many serious flaws so that the Iranian regime can never threaten the world with nuclear weapons," Trump said.
With Congress the next battlefield over Iran policy, diplomats say they have observed US lawmaker reluctance at being seen as responsible for walking away from the pact.
"Many senators are looking for a middle way," said one Western diplomat. "They don't want to kill the agreement."
The 2015 Joint Comprehensive Plan of Action (JCPOA) curbed Iran's nuclear program in return for sanctions relief.
It was signed by Iran, Germany, and UN Security Council permanent members Britain, China, France, Russia and the United States.
Trump could have scuppered the deal himself, by declining to waive the sanctions when they came up for review in September.
Instead, his decertification move set the clock ticking on a 60-day period during which Congress can choose to re-impose the sanctions.
Tehran has warned such action would mean Washington had broken its end of the bargain, and thus likely signal the end of their own compliance.
US Secretary of State Rex Tillerson said the administration is not urging Congress to impose new sanctions.
"Obviously, if they do that, that does then put the JCPOA agreement in question," Tillerson said.
Congress could also "do nothing," and allow the deal to stand as is, he added.
Republicans, who are in the majority in Congress, have for years denounced the pact, which was brokered during Barack Obama's administration.
When the deal was struck, Congress passed the Iran Nuclear Agreement Review Act (INARA) that gave US lawmakers a say in managing the accord.
This includes a requirement for the president to certify Iran's compliance with the accord every 90 days, and an option to slap sanctions back on Iran with a simple majority vote.
Lawmakers are hesitant about re-imposing the sanctions, including restrictions on Iran's vast oil sector, that had severely hobbled the country's economy, but senior Republicans appeared keen to tighten the screws in other ways.
After Trump's announcement, House Foreign Affairs Committee chairman Ed Royce said that "in the coming weeks" the House will vote to boost non-nuclear sanctions.
Senate Foreign Relations Committee Chairman Bob Corker said it "might feel good for a second" to shred the deal, but he stressed the need to keep allies on the same page.
One option unveiled Friday by Corker and Iran hawk Senator Tom Cotton is an amendment to INARA that would toughen Iran's compliance requirements and address "deficiencies" in the deal.
The proposal would target the pact's "sunset" provisions that would gradually allow Iran to advance its uranium enrichment program from 2025.
According to a summary, the US would reimpose its pre-deal sanctions on Iran if it did restart enrichment, even if this was allowed under the JCPOA.
"I think that we have provided a route to overcome deficiencies and to keep the administration in the deal, and actually make it the kind of deal it should have been in the first place," Corker said.
Diplomats have expressed worry that tweaking INARA could jeopardize the agreement, and warned that the US unilaterally abolishing the "sunset" would make it harder to negotiate with allies that back the existing agreement.
It remained to be seen whether there was enough support in Congress for the amendment, which would require a bipartisan majority in the Senate.