For someone who just lost one of his two jobs, Gary Samore was in remarkably good spirits when I called him at his office at Harvard University. Samore had just stepped down from his position as the president of United Against Nuclear Iran (UANI), an influential bipartisan group that opposes the Iran nuclear deal. The reason for the change was buried at the bottom of a very strange and very surprising UANI press release announcing his replacement: Samore now supports the nuclear deal.

Samore's journey on the Iran nuclear program is an interesting one. He has studied it for decades, worked on it as a senior arms control official in the Clinton and Obama administrations, and left government in 2013 to join Harvard and to preside over UANI. He long shared UANI's official position of skepticism toward the idea that an acceptable nuclear deal could be negotiated with Iran. That carried a lot of weight in the arms control community, where he is considered a leading authority and a technocrat.

"I think [the deal] is better than the alternatives, and that's the only way that one can grade these things"

But in April, when the US and other negotiating countries released a framework spelling out the deal's basic points, Samore surprised a lot of people by declaring it, in a Foreign Affairs article, "solid." He still had some reservations, but those apparently fell away in July, when the US and world powers released the complete agreement.

Though Samore came around to the Iran deal, the organization he led, UANI, did not. The group announced on Monday that Samore was stepping down as president (he is still a member), to be replaced by former Sen. Joseph Lieberman. It was a big deal — the New York Times covered it — and it seemed significant that the head of an anti-deal organization had come around in favor of the deal. It also seemed significant that, rather than the organization following their president's lead, they replaced the widely respected arms control expert with a former politician known for his hawkish views.

I called Samore to ask him about what had happened, as well as what he'd learned from the experience, both about the Iran nuclear deal and about the politics of it. He had some interesting and often blunt things to say. While he was careful not criticize UANI, he said he'd come out of the past year worried that "the American capacity to have a reasoned debate about national security issues has really been damaged by the polarization in Washington. ... There are still experts, but their voices are really muted by the politics."

The decisive moment for his presidency at UANI came, he said, when the group decided to run an ad campaign encouraging Congress to kill the deal. "I'm skeptical that we can reject this agreement and negotiate a substantially better deal within any kind of reasonable time frame," Samore said. What follows is a transcript of our conversation, lightly edited for length and clarity.

Max Fisher: Take me back to earlier this year, before the framework of the nuclear deal came out in April. Your view at the nuclear deal at that point was — is it fair to say skeptical?

Gary Samore: Very fair. I was extremely skeptical that an agreement was possible because [Iranian Supreme Leader Ali] Khamenei was laying out public red lines that I knew the United States could not accept. Remember that he was saying things like, "We won't accept any dismantlement of our existing centrifuges, we won't accept any restrictions on research and development, we must have an industrial-scale enrichment program within a matter of years." I made the mistake of believing him! In April [when the framework terms were released], it was clear that his red lines were simply bluster. "There is a genuine consensus among the experts on the desirability of a diplomatic agreement"

Max Fisher: Before the framework came out, were you skeptical of the idea of a nuclear deal itself?

Gary Samore: Oh, no, I've always been in favor of a deal. I think that diplomacy is one of the tools that we use to delay the problem, to manage the problem, contain the problem. Just like all the tools we have: sabotage, sanctions, military force — these are all tools for delay.

Max Fisher: When the framework came out in April, the piece you wrote in Foreign Affairs expressed some reservations but was overall pretty positive.

Gary Samore: I was pleasantly surprised that the Iranians had accepted physical constraints on their nuclear program, completely contrary to the red lines of the supreme leader. And at least in principle, they agreed to inspection and enforcement mechanisms that looked pretty powerful, on paper. And what's happened now is that those details have been codified in the final agreement. The big difference between [the framework agreed to in the Swiss town of] Lausanne and the final deal are the details that spell out the verification and enforcement mechanisms.

Max Fisher: When you saw the final terms come out in July, did that resolve, in your mind, the lingering concerns you'd had after the framework?

Gary Samore: Well, not really, but it improved the deal. The lingering issues do remain. First of all, the deal allows Iran to retain a larger enrichment program that I would prefer. Our opening position was [for Iran to have] a few hundred centrifuges, no research and development of more advanced machines, and limits that extended from 20 to 25 years. "There are still experts, but their voices are really muted by the politics" In order to get a deal, we've accepted several thousand centrifuges, a program of research and development, and limits that expire in 15 years. The second big concern I have about the agreement is really duration. For the first 15 years, the agreement has very good constraints on Iran's ability to produce fissile material, as well as verification and enforcement provisions. But after 15 years, those expire. And we don't know what Iran will be like in 15 years.

Max Fisher: Could we have gotten a better deal?

Gary Samore: It's very hard for me to answer that question. Unless you're actually sitting in the room, doing the back-and-forth, it's very, very difficult to say with any confidence that we could get a substantially better deal. When I say substantially better, I'm talking about much more dismantlement of Iran's enrichment program, unlimited duration or a longer duration, and more robust challenge inspections [of undeclared facilities]. I'm not talking about — I mean, the difference between 6,000 centrifuges and 5,000 centrifuges is trivial. Yes, you could probably get slightly different terms. We could have allowed them to keep a larger amount of low-enriched uranium, in exchange for having fewer centrifuges. There are all of these trade-offs embedded in the deal. But I don't consider these kinds of details significantly better.

Max Fisher: It sounds like what you're talking about, in terms of any different deal we could've gotten, is more about pushing around the numbers than getting a deal that looks fundamentally different.

Gary Samore: With the leverage that we have — which is economic sanctions and political pressure — I don't think we can achieve a dismantlement of their program, unlimited duration, "anytime, anywhere" inspections. I just don't think those are possible under current circumstances. Their economic situation would have to be much more dire, or we would have to be willing to use a military ultimatum to get those kinds of concessions from Iran.

Max Fisher: You're in academia now. Looking at the black-and-white text of the deal, what's in it and what's not in it, what letter grade would you give it?

Gary Samore: I would give it a passing grade. You have to compare it to the alternatives. The agreement has strengths and weaknesses. But then you weigh those strengths and weaknesses against the alternative. And I'm skeptical that we can reject this agreement and negotiate a substantially better deal within any kind of reasonable time frame. Over a period of years, we might be able to reassemble the sanctions pressure and build up enough pain so that Iran returns to the bargaining table, but at that point they're going to have another 20,000 centrifuges! And I don't know that we could get a substantially better deal.

Max Fisher: I can't help but notice that you avoided picking a specific letter grade. I'm not going to push you on choosing one, but I'm curious why that is, if there's something about assigning a specific value here that you're uncomfortable with.

Gary Samore: I think [the deal] is better than the alternatives, and that's the only way that one can grade these things. There's no absolute measurement. All you can say is that it's a better deal, in my view, with all its flaws and warts, it's a better deal than the likely alternative if we'd rejected it.

Max Fisher: Let me take you back to April again, when you published your Foreign Affairs piece praising the framework of the deal. Can you talk about what sort of reaction you got to that? Were people surprised to see the president of United Against Nuclear Iran taking this position?

Gary Samore: I don't think so. We've always had a healthy, open debate within UANI about what would be an acceptable agreement. Obviously, there was no need to make a final decision until the agreement was finalized. The purpose of UANI, the objective of UANI, was to have a bipartisan group that supported sanctions as the mechanism necessary for achieving an acceptable diplomatic outcome. I'm totally convinced that without sanctions pressure — and I think that UANI made a real contribution to achieve that pressure — we wouldn't have any deal. The only way to explain this agreement is Iran's need for sanctions relief.

Max Fisher: Was the discussion within UANI, at the time, that if the final deal came out and supported it, then you would step down?

Gary Samore: [UANI CEO and former Bush administration official] Mark Wallace and I agreed that if we ever reached the point where there was a disagreement between me and the rest of UANI over whether to support or oppose the agreement, then it wouldn't be sustainable for me to continue as president. But we didn't actually make that decision until this weekend, when UANI decided to launch an ad campaign to urge Congress to oppose the agreement.

Max Fisher: Was that a decision that you were involved in?

Gary Samore: I was involved in the sense that I knew what was being discussed. I understand their reservations, and they're within their rights to advocate that Congress reject the agreement, even if I don't share that view. I think they're going about it in a way that's reasonable and respectful.

Max Fisher: This whole thing is sort of weird, though, right? UANI exists to prevent a nuclear Iran, and its president, who is a very distinguished arms control expert, thinks that this diplomatic agreement is the best way to do that. So you would think that what would happen is that UANI would follow the advice of its president, who is also a respected expert. But instead what happens is that the president steps down and is replaced with a politician, who is not considered an expert and opposes the deal. What should we make of all this, because it seems quite puzzling from the outside.

Gary Samore: To me it doesn't seem puzzling. They make a different judgment, at the end of the day, about what constitutes the terms of an acceptable agreement. I've been working on Iran's nuclear program since the Reagan administration. My expectations for what diplomacy can achieve are pretty modest. Maybe other people have higher expectations.

Max Fisher: I think a lot of people look at the groups lined up against the deal and conclude that many of these groups would oppose any deal. And some people seem to see what happened at UANI as evidence of this.

Gary Samore: I don't agree with that. Maybe their expectations were unrealistic, but I do not think that UANI would have opposed any deal. I've had a lot of conversations with Mark [Wallace], and I think there could have been a deal that he would have supported — maybe not embraced, but was good enough. But that deal turned out not to be negotiable. I think the same is true with [Israeli Prime Minister Benjamin Netanyahu]. I think Bibi was relatively comfortable with our opening positions, after the interim agreement was reached [with Iran in late 2013]. I think what alarmed him is that we made compromises to make a final agreement.

Max Fisher: More generally, to the degree that there are disagreements among experts over the nuclear deal, are those agreements over narrow, specific issues of nonproliferation best practices, like what's the best inspections timeline, or do they tend to be about something more fundamental?

Gary Samore: Most of the people I deal with are genuinely supportive of a diplomatic solution. There are very few people who believe that we're at the point where we should be using military force or regime change. There are very few people who say that should be our policy. There is a genuine consensus among the experts on the desirability of a diplomatic agreement. And then it really comes down to how you weigh the importance of different elements, and where you should or shouldn't make concessions. At least among the experts, I think it is a real argument about the details.

Max Fisher: Over the past year or so, as this has all played out, what do you feel you've learned about the politics of this nuclear deal?