On Saturday, President Donald Trump brought the United States into Israel’s war against Iran. American planes and submarines struck three sites in Iran, including two nuclear enrichment facilities—at Natanz and Fordow—and a complex near Isfahan that was believed to contain stores of uranium. The Israeli government had been pushing for Trump to strike, in part because the Fordow site was believed to be reachable only with American aircraft and weaponry. Prior to Israel’s attack on Iran, which began a little more than a week ago, Trump had repeatedly stated that he wanted to make a nuclear deal with Iran, despite, in his first term, having pulled the U.S. out of Barack Obama’s nuclear deal with the country.

On Saturday night, in a televised address, Trump claimed that the three sites were “completely and totally obliterated,” and said that Iran must now “make peace,” warning of more attacks if they did not. The actual extent of the damage is not yet known, nor is it clear if and how Iran will retaliate. (Trump had announced on Thursday that the decision on whether to strike would be made “within two weeks” and that there remained a possibility of negotiation.)

Late on Saturday, I spoke by phone with James M. Acton, the chair and co-director of the Nuclear Policy Program at the Carnegie Endowment for International Peace. During our conversation, which has been edited for length and clarity, we discussed why even a successful strike might do less damage to the Iranian nuclear program than the Trump Administration hopes it will, whether the action could lead to a larger conflict with Iran, and why Trump’s decision to pull out of Obama’s nuclear deal wrecked the best chance to curtail Iran’s nuclear program.

What are your first impressions of what happened tonight?

I’m kind of appalled, to be honest, as an American citizen—appalled that the President would start military action without congressional authorization. That’s my immediate reaction. But, as a nuclear-policy analyst, I’m very worried that this is the beginning of a prolonged conflict, not the end of one.

Why is that?

In a lot of the coverage I have been seeing, and in a lot of the advocacy for what President Trump ended up doing tonight, there has been the impression that this would be a one-and-done thing—the President would authorize a strike, Fordow would be destroyed, the Iranian nuclear program would be ended, and it would be a very quick, completely decisive military intervention. There’s two reasons why I think that’s wrong. The first one is immediate Iranian retaliation. Iran has many short-range ballistic missiles that can reach American bases and American assets in the region. Israel has not particularly targeted that infrastructure. It’s been primarily focussed on Iran’s longer-range missiles that can reach Israel. So I’m expecting to see some pretty dramatic attempted retaliation by Iran, and I think that puts enormous pressure on the President to respond again. That is the first pathway to immediate escalation in the short term.

In the slightly longer term, I believe it’s very likely that Iran’s going to reconstitute its nuclear program. I think Iran is likely to withdraw from the Nuclear Non-Proliferation Treaty (N.P.T.) and thus kick out inspectors. The N.P.T. prohibits non-nuclear-weapon states, such as Iran, from acquiring nuclear weapons, and requires them to accept International Atomic Energy Agency (I.A.E.A.) safeguards, such as inspections, to verify that commitment. That puts us in the position where an American President or Israel might start striking Iran again and again.

I don’t want to speculate about exactly how successful these strikes were, but, if the strikes did what Trump has claimed, how much of a blow would that be to the Iranian nuclear program?

My answer may be a slightly unsatisfactory one, but it depends on how much else is destroyed. There are two key things that worry me. The issue is not just destroying fixed sites. Iran also had a bunch of highly enriched uranium that was once believed to be stored in tunnels underneath Isfahan. And the Iranians have claimed that they’ve removed that material. And then, secondly, there’s a whole bunch of components for building centrifuges that were being monitored when the Joint Comprehensive Plan of Action (J.C.P.O.A.) was enforced and are now no longer being monitored.

The J.C.P.O.A. is the 2015 nuclear deal, which was negotiated by the Obama Administration, and which exchanged a lessening of sanctions on Iran for nuclear inspections and limits on enrichment, and which Trump pulled out of in 2018.

Exactly. If the highly enriched uranium and the centrifuge components are small, that means that they’re portable. They can be moved around the country; they can be hidden. So, if what the U.S. has done is destroy the big sites that we know about, the enrichment facilities, but hasn’t destroyed the highly enriched uranium and the centrifuge components, I think Iran can probably reconstitute relatively quickly, perhaps within one or two years. It’s very hard to put an exact time on this. If the operations have managed to destroy some of the highly enriched uranium, or all of the highly enriched uranium, and the centrifuge components, then the reconstitution timeline is likely to be longer. What I would point out is that under any scenario the reconstitution timeline is going to be much shorter than the ten to fifteen years of the J.C.P.O.A. That’s how long the deal was supposed to last for. It is also worth pointing out that people argue the J.C.P.O.A. was a bad deal because it only lasted that long. Even that was a bit misleading.

Why?

Because some parts of the J.C.P.O.A. lasted twenty years, some lasted twenty-five years, some actually were indefinite. It was actually quite a complicated arrangement, the way the J.C.P.O.A. phased out over time. Limits on enrichment and uranium-stockpile sizes lasted ten or fifteen years. The I.A.E.A.’s right to monitor centrifuge components lasted twenty years. The prohibition against weaponization activities had no time limits. But, even under the ten to fifteen years that was often quoted, we’re now likely dealing with a reconstitution timeline under any scenario that’s substantially shorter than that.

A central point you have made, which I have seen you make in the past, is that the alternative to this strike and the Israeli action was not nothing but was in fact the deal that Trump exited in 2018. Was that deal succeeding?

I think the J.C.P.O.A. was working very well. The U.S. intelligence community assessed that Iran was complying with the deal. Iran’s program was heavily limited, and it was heavily inspected. To my mind, it was working very well when Trump pulled out. And I do think there was a slim but real opportunity for diplomacy over the last few days. Obviously, there was no possibility of reconstituting the J.C.P.O.A. But you had this interesting situation where Israel had started an attack, it couldn’t destroy everything in Iran, including but not limited to Fordow, and the American threats gave Trump some leverage. And Trump at times appeared interested in trying to use that leverage to negotiate. I do feel there was some kind of window for diplomacy there. I’m just very sad that that window was never taken, and there wasn’t a good-faith attempt to try and take advantage of it.

The lack of good faith was from Trump, or from the Iranians, too?

We don’t know. But what I would point out is that a serious negotiation can’t be done in forty-eight hours or however long it was since Trump announced that he was going to give the opportunity for diplomacy. He said this week that he would make a decision within two weeks. So my feeling is that there was never any real attempt on the part of the U.S. to follow up on that and actually try to negotiate some kind of diplomatic settlement here.