A compromise allowing the US Congress to vote on a nuclear deal with Tehran may prompt Iranian negotiators to drive a harder bargain, but does not drastically weaken President Barack Obama's ability to deliver on a final agreement.
For months Obama resisted attempts led by Republicans and some Democrats to open an agreement with Iran to congressional approval. On Tuesday he backed down in the face of mounting bipartisan support for the bill, which gives Congress at least 30 days to review a final deal during which time Obama would be unable to waive or suspend many US sanctions.
Negotiators for Iran and six major powers are trying to ensure Iran does not acquire an atomic bomb by securing an agreement by June 30 under which Iran would curb its nuclear program in exchange for relief from international sanctions.
"If I were an Iranian negotiator, I would walk into that room and say 'you told us all along you were going to stop legislation,'" said Richard Nephew, a former US negotiator with Iran now at Columbia University.
"'How can you guarantee us that we’re not going to have this problem when we bring the deal forth?'"
"Will it be fatal? No," he added. "It’s going to make things a lot harder, a lot more complicated, a lot more difficult for the (US) negotiating side."
While it is largely a US-Iranian affair, the talks also include Britain, China, France, Germany and Russia. The European Union is also a key player in the process, which resulted in a preliminary deal on April 2 after marathon talks.
Since then, sharp differences in interpretation over the terms have emerged, with Iran saying sanctions must be lifted immediately after a deal is reached and Washington insisting the sanctions will be phased out over a longer period.