Transcript for What's Next for the Iran Nuclear Deal?
We'll turn to that nuclear deal with Iran reached yesterday after a marathon negotiation in Switzerland. President Obama called it an historic move that could make the world safer but many in congress are skeptical and popses of tough negotiations ahead. ABC's terry Moran is in Switzerland where he sat down with America's chief negotiator secretary of state John Kerry. Good morning, terry. Reporter: Good morning, George. Well, what we witnessed happened here over the last few days and nights would have been unthinkable a few years ago, Americans and Iranians and think of that poisoned history there, they were in the same rooms. They were negotiating, arguing, bargaining, working together to get the framework of a nuclear deal. This morning, a hero's welcome in Tehran for the country's top nuclear negotiator. They were partying in the streets when the deal was announced last night. Hoping for desperately needed economic relief from those crippling sanctions. President Obama facing a far more skeptical congress saying those sanctions brought Iran to the table and claiming this deal as a win for the U.S. It is a good deal, a deal that meets our core objectives. Reporter: Iran agreeing to unprecedented inspections and monitoring of its nuclear facilities for at least 20 years and also rolling back its programs, dismantling equipment, rebuilding major plants to ensure they're only for civilian uses. In exchange, sanctions against Iran will be lifted over time. But Iran will still be able to research and develop advanced nuclear technology and make nonweapons grade uranium. Critics in congress determined to kill this deal. This deal is going to threaten America's national security interests. Reporter: And it's far from being a done deal. Could this whole thing still fall apart? Of course, it could. What's the chances of it getting all the way? I don't have any way to make that prediction. Reporter: 50/50? I'm not going to play that. This is a way of making the world safer. Reporter: So the weeks and months ahead are crucial. Critics and hard-liners in both countries will try to kill the deal and there are a lot more negotiations ahead. There sure are. You showed those cheering in the streets of Tehran. They took the unprecedented step of showing president Obama give that speech live but importantly Iran's supreme leader has not weighed in. Reporter: He has not. We are expecting to hear from president rouhani but have not heard from ayatollah khomeini and he is the man who is the leader and will decide which way this country goes. He has supported these negotiations because of those young people that you see in the streets. Iran's a country where you can't really use a credit card, where you can't download an app and as they head into the mid-21st century that is unsustainable and decided to do this to save their regime. Thanks very much. Much more on this Sunday on "This week."
This transcript has been automatically generated and may not be 100% accurate.