The first person I called when negotiators in Vienna released the final text of the Iran nuclear deal was Aaron Stein, a nuclear nonproliferation expert at the Royal United Services Institute. Stein is a prolific writer and commenter on nuclear issues, and particularly on Iran's nuclear program. (He is also doctoral fellow at the Geneva Centre for Security Policy and a non-resident fellow at the Atlantic Council.) And he is a die-hard wonk — someone who cares first and foremost about understanding the issues, rather than about picking a side.

Stein walked me through how the Iran nuclear deal works, what it does, and his assessment of it. That assessment was very positive, he told me: The deal "exceeds in all areas." Under this agreement, if Iran tries to build a bomb, "the likelihood of getting caught is near 100 percent." As a result, "it makes the possibility of Iran developing a nuclear weapon in the next 25 years extremely remote."

What follows is a transcription of our conversation, edited for length and clarity.

Max Fisher: It's worth remembering that what this deal is really supposed to be about is preventing Iran from getting a nuclear bomb. So can you just talk me through, if Iran wanted to get a bomb, how they would do that? And how good is this deal at stopping them from that?

Aaron Stein: They would do Fordow 2.0. [Fordow was previously a site of secret Iranian nuclear development.] They would siphon off uranium from an undeclared mine, which we can get to in a second why that's not really possible [under the deal]. "This will take us into 2040" Then they would build centrifuges without us knowing, because a centrifuge facility is tiny. You don't really pick them up; we've never really been able to find them when they are up. We can get around that [centrifuge problem] if we know where every centrifuge is made, if we know where the machines that make them are sitting. And in this deal, those factories are also subject to monitoring. And that's really where the deal exceeds in all areas. It's a 25-year sunset on this, so this will take us into 2040. So it's not the next president's issue. "The intention of this agreement is to take the weapons option off the table for the next 25 years, and the agreement does that"

Max Fisher: You've looked over the Iran deal, you've been following these negotiations and the Iran nuclear issue for a long time. Is this a good deal?

Aaron Stein: It exceeds or is directly in line with everything in the US fact sheet that was put out [in April]. I thought the US fact sheet was a great deal, and I think this is a good deal. When I say that, I mean that it's a very good nonproliferation deal. If you want it to focus on the problems with Iran running around in Iraq or Syria, this deal is not for you. If you are focused on the nuclear issue specifically, it's a very good deal. It makes the possibility of Iran developing a nuclear weapon in the next 25 years extremely remote. It would require a Herculean effort of subterfuge and clandestine activity. It's important that it puts inspections in place. Inspections are not always designed to catch you red-handed but rather to elicit a response about what it is that you are up to. The threshold for pain is so high that you don't want to break the rules, and I think this puts that in place while also making it extremely difficult to cheat.

Max Fisher: The last time we talked, in April when the framework came out, you really emphasized inspections as something that was crucial for this. You seemed to have a very positive take on how it looked in the framework. Is that still how you feel, looking at the final deal?

Aaron Stein: Yes. One thing that was not in the framework deal that's fleshed out now is the thing with flow forming machines. Flow forming machines are how you make centrifuges. If you have one stashed away out in the middle of the desert in a facility, we would have no idea. In the agreement, they have to account for all of their flow forming machines, give us a list of where they are, and then put them under monitoring. The counter to that is they just won't tell us, they won't declare everything. That's to be expected, so don't trust that. "We should know — we helped develop those fields in the 1970s" Then the fall back on that is that you monitor the uranium as it comes out of the ground until it goes in [the Iranian nuclear facility at] Natanz and then when it comes out of Natanz. If all of a sudden a barrel of uranium at a conversion facility doesn't show up, we'd know. They have an accounting of what comes out of the ground; they have an accounting of what has been refined at the processing plant. They have an accounting of what's been converted, then they have an accounting of what shows up at Natanz, and then they have an accounting of what comes out the back end. So if Iran has a little centrifuge facility stuck out in the middle of nowhere, they need uranium for it. But if all of sudden uranium numbers don't match up, inspectors are going to start asking what happened to that uranium. And Iran only has two mines. It does not have rich uranium deposits, despite its claims to the contrary. We should know — we helped develop those fields in the 1970s. It's not high-quality uranium and there's not a lot of it, so we should be able to watch it. "You have a very small enrichment program, operating in perpetuity, that can basically be a fig leaf allowing Iran to say it's kept its enrichment program"

Max Fisher: What else has changed that's significant between the framework and the final deal?

Aaron Stein: We have a lot more clarity about conversion. [Iran is only allowed to keep a very small stockpile of low-enriched uranium on hand, so will have to convert any excess to a different form.] Iran is not very good at a lot of what it does because it's using antiquated, 50-year-old technology reverse-engineered from Chinese designs. One of the proposals was always that the Russians, the Europeans, or we would help them with some of these things because it was in our best interest. It looks like, on conversion, they will get some help on this so that they can take some of the LEU that they produce in Natanz, turn it into fuel plates, and then put it into fuel that they can then burn themselves. Now this is the leap of faith: if this becomes the basis for what will become Iran's future nuclear program, that you have a very small enrichment program, operating in perpetuity, that can basically just be a fig leaf allowing Iran to say it's kept its enrichment program. Even though it's completely minuscule in size, very well-monitored, and nothing really to call home about.

Max Fisher: Let me ask you about sanctions and how they come off. I know this was a big question mark after the framework deal: the timing of it, mechanisms for removing the sanctions, and then of course mechanisms for reintroducing them. How does this look in the final deal?

Aaron Stein: Make no mistake about it, this is a pathway for them basically to have all the major sanctions against them, related to the nuclear issue, removed. Frankly, I don't see anything particularly wrong with that; sanctions are a coercive tool to force a policy change. The policy change we wanted was to place limits on Iran's enrichment program in perpetuity. We got that, and so I don't see that being a big problem. I was always skeptical of "snapback" [the provision that any sanctions would snap back into place if Iran is caught cheating] because of the likelihood that China or Russia would veto any such move to go back. It looks like they were able to get around that. But once these sanctions start to come off, I think it will be very difficult to then put them back on, even if the snapback is relatively strong on paper.

Max Fisher: How long does it take for sanctions to come off, then?

Aaron Stein: Adoption, it says here, will occur 90 days after the endorsement by the UN Security Council. Once the UN Security Council endorses it, we have 90 days in which they have to meet all their obligations, and then these sanctions will start to come off. My understanding is that they begin to be removed immediately, particularly the EU sanctions and the UN Security Council sanctions. Those will be replaced with this new UN Security Council resolution. This is all contingent on the IAEA track being resolved, which it looks like it will. That was a concession, by the way, to the Iranians. They're using Iranian language in the framing of the IAEA, calling it a road map. It creates a pathway for them to wiggle out from underneath the PMD issues, which if we're going to solve this you have to get over the PMD issue.

Max Fisher: Right, PMD — "possible military dimensions," the idea that Iran has to reveal any past work it's done on military elements of a nuclear program. In other words, to disclose any past work specifically on getting a bomb. I know that was a big issue in the negotiations, and it looks like it's going to be a big political issue now. How important is that?

Aaron Stein: A lot of it has focused on Parchin. [Iran had conducted some past nuclear work at its military facility at Parchin.] Parchin is a red herring; I have no idea why the IAEA is so hung up on Parchin. They won't find anything there — it's completely stripped of anything of value. The real concerns about Iran's PMD were weapons-specific tests. I'm talking about the development of a shock implosion system to generate a nuclear explosion and the conducting of weapons-specific mathematical and computer modulate tests.

Max Fisher: So the issue for the nuclear deal is that, in order for the deal to go forward, Iran has to satisfy the IAEA that they have sufficiently disclosed information about past weapons research?

Aaron Stein: Yes. They'll find some creative language to get around this, there's no doubt in my mind. There are very few people who seriously believe that Iran wasn't up to no good between 1985 and 2003. The intention of this agreement is to take the weapons option off the table for the next 25 years, and the agreement does that. In the past, the way the IAEA resolved this is by using language that didn't call Iran a liar flat-out, but rather said that Iran's explanation is not inconsistent with how this may have happened, something along those lines. The agency will basically cast out on Iran's explanations without saying so, or say so in a very diplomatic language.

Max Fisher: It's looking like a big fight in Washington over the deal, and something that critics have been expressing concern about for a while, is this provision limiting inspectors to "managed access" or certain military sites.

Aaron Stein: That was a red herring from the beginning. The only inspection protocol where you're going to have writ large access to every military site would be the Iraq-style inspections that we got after the 1991 Gulf War. What country is going to give you access to their military sites that are not affiliated with the nuclear issue? This was all about Parchin. Will they get access to that little shack out in the boonies of this large base to go look at what used to be a detonation chamber that doesn't exist anymore? The detonation chamber is not there, the ground around it has been razed, they're not going to find anything at Parchin. This came down to a pissing contest about whether or not we could go walk into Parchin, which is irrelevant. In the deal they're going to give managed access to Parchin, and you know what? We're going to lose on this because they're not going to find anything at Parchin. All of this will come down to nothing. I think what will happen is the IAEA will submit a detailed questionnaire and Iran will respond, and then the agency will review those responses and then draw a conclusion from them.

Max Fisher: You think it's likely that the IAEA will sign off by the deadline?

Aaron Stein: I think so, yes. The IAEA was involved in this [deal], particularly with these final stages. This will not hold up the implementation of the deal.

Max Fisher: Are there fights ahead that could hold it up?

Aaron Stein: There are always fights over implementation. That's why the dispute resolution mechanism is put in there. In the coming days we'll see craziness from both sides about how the other side is violating the agreement — that's to be ignored. The Russians to this day say that we didn't implement START [the 1991 nuclear treaty] because we put this specific shroud over the top of our warheads when they come to go snooping around them.

Max Fisher: One of the big questions of the last few months was how they would deal with the issue of, should Iran get caught cheating, how you bring back sanctions. And it looks like they had a pretty solution with this "snapback" process that would trigger in the UN Security Council. Let's say that works, but Iran just shrugs off the sanctions and continues with its cheating. What then? At what point do you do something past sanctions, whether it's military action or something else?