For a quarter century, Uzi Arad was one of Mossad’s top spies. He rose to become the director of its intelligence division. He later gained fame as a top aide to Prime Minister Benjamin Netanyahu, the Likud Party leader who has campaigned longer and harder against the Iran nuclear deal than almost any other leader. Arad, who served as the national-security adviser from 2009 to 2011, broke with his former boss over the agreement. He travelled to Washington this week to lobby—primarily among Republicans in Congress—to save the controversial agreement at a pivotal juncture.

Next week, President Trump is expected to announce that he believes Iran is not fully complying with the accord that he dubs the “worst deal ever.” In a break with the five other world powers that negotiated the deal, he is expected to say that the historic agreement is not in the U.S. national interest. Trump’s long-awaited Iran policy—nine months in the making—concludes that Tehran has violated the spirit of the deal because of its missile tests, support for terrorists, intervention in Middle East conflicts, and human-rights abuses. Trump will instead announce a comprehensive strategy to deal with all of Washington’s issues with Tehran—reversing the Obama Administration’s approach to eliminate the nuclear threat as the first step in negotiations on all flash points.

In the run-up to Trump’s speech, Washington is awash with last-ditch efforts to save the deal. How Congress responds will be vital. It has sixty days to decide whether to re-impose sanctions. If Congress does not impose sanctions, the deal could drift in a kind of policy purgatory.

Arad has long experience tracking Iran. In secret negotiations, he interacted with Iranians in the mid-nineteen-eighties, as the revolutionary regime was hunting for arms during its long war with Iraq. He had the Mossad account for the Iran-Iraq war. I talked to Arad as he wrapped up his efforts to save the deal on Thursday. The interview has been condensed and edited for clarity.

Why are you doing so much to preserve a deal that your own Prime Minister has rejected?

I have never been opposed to the deal. There were two ways of stopping the Iranian program. One was the direct approach—bombing. It is one of the easiest things to do. Big facilities, fixed facilities. If there is something that has been waiting to be bombed, it’s that. But that would have called for drastic action, so the preferred approach has always been to stop the program as a result of an agreement. I do not think that Israel should have come out against the principle of negotiations.

We could have gotten a better deal. I know that the initial negotiating positions of the five plus one, in their own assessment as to the give and-take, expected better results. But the dynamics of negotiations are such that you never know. And, besides, the Iranians were very good.

What would it cost to depart from the agreement now?

You would lose all those limits imposed on the Iranians. They could declare themselves still upholding the agreement with the other five [parties]. They could say, “We will abide by it. If America wants to walk out, let it walk out. Let them re-impose sanctions without assistance from some of the allies.”

Which parts of the accord did you think were weak?

The military sites. The fact that they are refusing, of course, makes you uneasy. This has got to be done; otherwise, the inspection is flawed. Very flawed. It’s difficult, as Iran is very big. Remember that [enrichment facilities] at Natanz and Fordo were supposed to be secret. The uneasiness over the possible existence of other secret sites should always be there. It’s a cat-and-mouse game, but it runs against the spirit of the agreement to have an inspection regime which leaves such a loophole, which they insist on, with Russian backing. That has to be corrected, because that is integral to the agreement.

The sunset clauses—that is a highly unstable situation to be in. That, too, has to be amended or through a supplement, because it is, again, it is against the declared purpose of the whole exercise. Agreements should not be renegotiated, they should be strengthened, and that has been done with previous arms-control agreements throughout history. There’s never been an agreement to end all agreements.

The missile issue, separately. Iran, from Day One, their delivery capacity has never had anything to do with air. They’re working on missiles. That is a very troubling thing that should be arrested. If there would be no nuclear capacity, there is no real justification for some of those missiles.

Iran, by and large, has complied with the more fundamental steps it had to take. Certain things at the margins can be corrected through diplomacy. At the moment, you don’t have the allies for anything—not for sanctions, not for improving on the agreement. And then you have to move to the other matters on the agenda—Syria, terrorism, and even missile development.

What kind of response have you had in Washington, especially in Congress? If Trump “decertifies” Iran, Congress would then have sixty days to decide whether to impose sanctions lifted as part of the deal.

It is interesting to see that they are reflective. Republicans, some of them, will not necessarily follow anything the President says one way or another. They keep some independence of action. They don’t like the condition in which they may be thrust into—making the unpleasant political choices that the President may want to avoid. So it was interesting to see the range of reaction.

How do your views reflect the thinking among the Israeli intelligence community and the Israeli foreign-policy community?

Qualitatively, it is the majority. What I did in the last few months is talk to people I think very highly of. One is very respected in the field of science but has been in the intelligence community, is a general by rank. Another is a very senior bureaucrat from the atomic-energy establishment. A third one is a former head of military intelligence. All of whom, from Day One, did not think that the agreement was the catastrophe that it was described to be. Quite the contrary.

You mean by your own Prime Minister?

Yes. When the possibility of withdrawing by the U.S. became an option, or when the Israeli Prime Minister called for “fix it or nix it,” one of them said, in Hebrew—in Hebrew things always sound so much better—“it would be a folly” to do so.

What are your concerns about Iran’s ambitions in the region when it comes to the Shiite crescent or the land bridge to Lebanon? What are the prospects for a direct conflict, once Syrian war ends, between Israel and Hezbollah?

Without trying to demonize or criticize the Iranians, the policies they’ve been pursuing in the Middle East have been expansionist in the most unpleasant way. I don’t think you’ll find many Israelis who expected—if we’re coming to the end of the civil war in Syria—that the product would be an established Iranian military presence on Syrian soil, with proximity to Israeli borders.

Why are they doing that? Are they not afraid? If there were to be any hostilities, they would be sustaining a terrible blow. But yet they’re doing it.

What would a war with Iran look like—for either Israel or the United States?

At one point, in my dealings with my American friends, I proposed a game. I said, “Let’s exchange roles. We’ll plan the American military options. You plan ours in a war with Iran.” With all the toys in the American store, I started to plan sorties from Tampa, Florida, in which you come back in the evening to have pizza after you unloaded all that from high altitude. For Israel, it’s difficult, the military option. I talked to a commander of the [Israeli] Air Force and said how much my heart goes to those young pilots who exercise for this thing and had to fly very long [routes], with refuelling midair and sometimes flying very low. The very exercises were extremely demanding. We did practice, and it could have been done.