Brett McGurk, the Special Presidential Envoy for the Global Coalition to Counter ISIL. Photograph by Samuel Corum / Anadolu Agency / Getty

For the first time since its blitz across Syria and Iraq, in 2014, the Islamic State is on the defensive in both countries. Its caliphate, led by Abu Bakr al-Baghdadi, is shrinking. Its numbers are down. It hasn’t launched a new offensive since May, 2015. The new U.S. Expeditionary Targeting Force in Iraq—led by some fifty Delta Force commandos—has scored the first capture of a key ISIS operative, the Pentagon said on Tuesday. The Iraqi military, meanwhile, is tightening the noose around Mosul, an ISIS stronghold and the country’s second-largest city. In Syria, a fragile new ceasefire, which took hold last weekend between the government and the rebel opposition, has turned attention on the Islamic State.

Yet ISIS, also known as ISIL, has become a global phenomenon in the course of the past year, attracting pledges of fealty from extremist groups on three continents. It remains the world’s wealthiest terrorist organization, and the first to create its own state, from large swaths of both Iraq and Syria, with a capital in the Syrian city of Raqqa.

Brett McGurk, a diplomat who has been involved in U.S. operations in the Middle East since the 2003 invasion of Iraq, began his Washington career as a law clerk to the late Chief Justice William H. Rehnquist. He was one of the main architects of the U.S. military surge in 2006 and 2007, which pushed back Al Qaeda forces in Iraq. McGurk also led fourteen months of secret negotiations with Iran on a prisoner swap, which finally culminated in freedom for five Americans in January. He is now the Special Presidential Envoy for the Global Coalition to Counter ISIL. On March 1st, McGurk reflected on the American-led campaign against ISIS during a conversation in his first-floor office at the State Department, just hours before leaving for Iraq. The interview has been condensed and edited for clarity.

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Force and Territory

How strong is ISIS, militarily, today? At its height, it had some thirty-five thousand fighters, from a hundred and twenty countries.

Current assessment: about nineteen thousand to twenty-five thousand fighters in Iraq and Syria— the lowest assessment since 2014—divided fairly evenly, but dominated increasingly by foreign fighters. Suicide bombers are nearly all foreign fighters. Tunisians, Belgians, Saudis, Libyans, all coming into Iraq and Syria to blow themselves up. As the Syrian civil war really started going, this major attraction of foreign fighters began ticking up to twenty, thirty, forty, sometimes sixty a month of suicide bombers, which showed us that we had a supercharged global network on our hands. Suicide bombers are just really pernicious. Major military operations are usually led by a wave of suicide truck bombs. We just had a number of suicide bombers in Baghdad, in Shia mosques, trying to re-spark some sectarian conflict.

How are they still making it into both Syria and Iraq, most notably from Turkey? Why hasn_’t the world been able to stop them?_

It is much harder for them to get in now than it was even six months ago. We can track that by the numbers but also by the information we’re seeing from ISIL’s own sources. Their open sources—like Dabiq magazine—are saying, “Think about going to Libya now.” So we’re seeing a migration out of Syria, out of Iraq, because life is pretty horrible for ISIL inside Syria and Iraq. It’s much harder for them to get in, and, once they’re in, much, much harder for them to get out. The entire Syria-Turkey border, a year ago, was controlled by ISIL. Now it’s a ninety-eight-kilometre strip of border, and we’re going to work to make sure that continues to shrink.

How many people has ISIS lost in fighting and in airstrikes in the past two years? At one point, in 2015, the U.S. estimated that ISIS was losing a thousand fighters a month.

It’s in the tens of thousands, low tens of thousands.

Twenty or twenty-five thousand_?_

Around there, yeah.

If ISIS is weaker, why haven_’t the array of forces on the ground, particularly in Iraq, backed by dozens of daily airstrikes by the U.S.-led coalition,_ made more headway in ten months? The U.S. goal is to “shrink the core of ISIS in both Iraq and Syria,” but that still seems a very long way off.

From where it was in the summer of 2014, ISIL has lost forty per cent of its territory in Iraq. It’s lost Tikrit, an iconic Sunni city. It lost Ramadi. It’s lost its connections between Mosul and Syria, losing Sinjar and a number of critical road connections. ISIL is increasingly shrinking. It takes time. It takes intelligence. It takes relationships. It takes ourselves getting established and reëstablishing networks, which we had to do.

And in Syria? What percentage of territory has ISIS lost there?

Again, it’s increasingly squeezed. Its connection from Syria, its main connection into Iraq and the Tigris River Valley, has been severed over the last week. We severed it by working with a diverse force, about six thousand men—about forty per cent non-Kurd, sixty per cent Kurd—working together to take the town of Shaddadi. We thought the operation would take about six weeks. It took about six days. Shaddadi was a stronghold of ISIL. When ISIL took Sinjar Mountain, in 2014, and captured thousands of Yazidis and Yazidi women, it brought them to Shaddadi to market them off. It was the heart of their perverse caliphate.

So, in Syria, they are increasingly under pressure. Syria is a different situation from Iraq, of course. In Iraq, we’re working with the government, with an army. In Syria, we’re not. So it’s much more complex, much more difficult. The overall territory that ISIL has lost in Syria is less than in Iraq, but the strategic nature of the territory is quite important. It’s the border with Turkey, and it’s cutting off these road connections between Syria and Iraq.

You have a time frame?

The over-all campaign to defeat ISIL globally—we’re talking a multi-year campaign. But I just don’t want to put a time frame on something as inherently uncertain as warfare.

Going After Their Financing

What is the state of ISIS’s finances? In December, an internal ISIS document leaked to the press claimed that it was forced to cut the salaries of its fighters by half. ISIS has many other sources of funding—from taxes, oil smuggling, extortion, and donations. What are its reserve__s today, and how have they been affected since the U.S. began striking ISIS oil tankers, in November?

We assessed that ISIL was taking in about a billion dollars a year: five hundred million dollars in oil and gas and five hundred million in other forms of revenue—taxes, extortion, antiquities, kidnapping. You have to go at it two ways. In the latter pot, you have to take away their territory. In the former pot, we have to determine how they are getting oil out of the ground, how they are moving it around, where it is going, and then how we can effectively target that. It took a great deal of very hard, very detailed intelligence work about how this is all working. It’s not as easy as, “Oh, let’s just go out and bomb the trucks.” That’s not going to be effective. We really wanted to rip out the spine of their ability to generate revenue.