[Editor’s Note: Below is Thomas Joscelyn’s testimony before the House Homeland Security Committee’s Task Force on Denying Terrorists Entry into the United States. The hearing is titled, “The Terrorist Diaspora: After the Fall of the Caliphate.” A version with footnotes will also be posted.]

Chairman Gallagher, Ranking Member Watson Coleman, and other distinguished Committee Members, thank you for inviting me to testify today concerning foreign fighters and the threat some of them pose to the U.S. and Europe.

The fall of Mosul and the likely fall of Raqqa won’t be the end of the Islamic State. The group has already reverted to its insurgent roots in some of the areas that have been lost. It also still controls some territory. The Islamic State will continue to function as a guerrilla army, despite suffering significant losses. In May, the Office of the Director of National Intelligence (ODNI) assessed that even though it was losing significant ground, the Islamic State “will likely have enough resources and fighters to sustain insurgency operations and plan terrorists [sic] attacks in the region and internationally” going forward. Unfortunately, I think ODNI’s assessment is accurate for a number of reasons, some of which I outline below. I also discuss some hypothetical scenarios, especially with respect to returning foreign fighters or other supporters already living in Europe or the U.S.

Recent history. The Islamic State’s predecessor quickly recovered from its losses during the American-led “surge,” capitalizing on the war in Syria and a politically poisonous environment in Iraq to rebound. Indeed, Abu Bakr al Baghdadi’s organization grew into an international phenomenon by the end of 2014, just three years after the U.S. withdrawal from Iraq was completed. Baghdadi’s men did this while defying al Qaeda’s leaders and competing with rival jihadist groups. This recent history should give us pause any time we hear rhetoric that sounds too optimistic about the end of the Islamic State’s caliphate. The enterprise has had enough resources at its disposal to challenge multiple actors for more than three years. There is no question that the Islamic State’s finances, senior personnel, and other assets have been hit hard. But it is premature to say its losses amount to a deathblow.

Uncertainty regarding size of total membership. While it is no longer at the peak of its power, the Islamic State likely still has thousands of dedicated members. We don’t even really know how many members it has Iraq and Syria, let alone around the globe. Previous U.S. estimates almost certainly undercounted the group’s ranks. In September 2014, at the beginning of the US-led air campaign, the CIA reportedly estimated that the Islamic State could “muster” between 20,000 and 31,500 fighters. This figure was “more than three times the previous estimates,” CNN noted. By December 2016, the U.S. military was estimating that 50,000 Islamic State fighters had been killed. By February 2017, U.S. Special Operations command concluded that more than 60,000 jihadists had perished. Two months later, in April 2017, the Pentagon reportedly estimated that 70,000 Islamic State fighters had been killed.

Taken at face value, these figures (beginning with the September 2014 approximation) would suggest that Abu Bakr al Baghdadi’s enterprise was able to replace its entire force structure more than two times over, while fighting multiple enemies on numerous fronts. This is, of course, highly unlikely. Even with its prolific recruiting campaign, it would be impossible for any cohesive fighting organization, let alone one under the sustained pressure faced by the Islamic State, to train, equip and deploy fighters this quickly. It is far more likely that the U.S. never had a good handle on how many jihadists are in its ranks and the casualty figures are guesstimates. The purpose of citing these figures is not to re-litigate the past, but instead to sound a cautionary alarm regarding the near-future: We likely do not even know how many members the Islamic State has in Iraq and Syria today.

The Islamic State is an international organization. Since November 2014, when Abu Bakr al Baghdadi first announced the establishment of “provinces” around the globe, the Islamic State’s membership grew outside of Iraq and Syria. This further complicates any effort to estimate its overall size. Some of these “provinces” were nothing more than small terror networks, while others evolved into capable insurgency organizations in their own right. The Libyan branch of the caliphate temporarily controlled the city of Sirte. Although the jihadists were ejected from their Mediterranean abode by the end of 2016, they still have some forces inside the country. Similarly, Wilayah Khorasan (or Khorasan province), which represents the “caliphate” in Afghanistan and Pakistan, seized upwards of ten districts in Afghanistan as of early 2016, but has since lost ground. More recently, jihadists in the Philippines seized much of Marawi, hoisting the Islamic State’s black banner over the city. Wilayah Sinai controls at least some turf, and is able launch spectacular attacks on security forces. It was responsible for downing a Russian airliner in October 2015. Other “provinces” exist in East Africa, West Africa, Yemen and elsewhere.

In May, the Office of the Director of National Intelligence (ODNI) reported that the so-called caliphate “is seeking to foster interconnectedness among its global branches and networks, align their efforts to ISIS’s strategy, and withstand counter-ISIS efforts.” Gen. John Nicholson, the commander of U.S. Forces-Afghanistan, has said that Wilayah Khorasan went through an “application process” and the Islamic State mothership provided it with “advice,” “publicity,” and “some financial support.” Although it is impossible to judge the extent of the Islamic State’s cohesion, as much of the data is not available, there is at least some connectivity between the group’s leadership and its “provinces” elsewhere. This is best seen on the media side, as the organization is particularly adept at disseminating messages from around the globe in multiple languages, despite some recent hiccups in this regard.

While their fortunes may rise or fall at any given time, this global network of Islamic State “provinces” will remain a formidable problem for the foreseeable future. Not only are they capable of killing large numbers of people in the countries they operate in, this structure also makes tracking international terrorist travel more difficult. For instance, counterterrorism officials have tied plots in Europe to operatives in Libya. This indicates that some of the Islamic State’s “external plotters,” who are responsible for targeting the West, are not stationed in Iraq and Syria. The U.S.-led air campaign has disrupted the Islamic State’s “external operations” capacity by killing a number of jihadists in this wing of the organization. But others live.

The cult of martyrdom has grown. A disturbingly large number of people are willing to kill themselves for the Islamic State’s cause. The number of suicide bombings claimed by the so-called caliphate dwarfs all other jihadist groups, including al Qaeda. In 2016, for instance, the Islamic State claimed 1,112 “martyrdom operations” in Iraq and Syria alone. Through the first six months of 2017, the organization claimed another 527 such bombings (nearly three-fourths of them using vehicle-borne improvised explosive devices, or VBIEDs) in those two countries. These figures do not include suicide attacks in other nations where Abu Bakr al Baghdadi’s loyalists are known to operate.

To put the Islamic State’s current “martyrdom operations” in perspective, consider data published by the Washington Post in 2008. According to the Post, there were just 54 suicide attacks in all of 2001, when al Qaeda’s “martyrs” launched the most devastating terrorist airline hijackings in history. The Islamic State currently eclipses that figure every month in Iraq and Syria, averaging 93 suicide bombings per month in 2016 and 88 per month so far in 2017. Many of these operations are carried out by foreign fighters.

These suicide bombers have been mainly used to defend Islamic State positions, including the city of Mosul, which was one of the self-declared caliphate’s two capitals. For instance, half of the “martyrdom operations” carried out in Iraq and Syria this year (265 of the 527 claimed) took place in the Nineveh province, which is home to Mosul. The “martyrs” were dispatched with increasing frequency after the campaign to retake the city began in October 2016, with 501 claimed suicide bombings in and around Mosul between then and the end of June 2017.

Some caveats are in order. It is impossible to verify the Islamic State’s figures with any precision. The fog of war makes all reporting spotty and not every suicide bombing attempt is recorded in published accounts. Some of the claimed “martyrdom operations” likely failed to hit their targets, but were counted by the Islamic State as attacks anyway. The U.S.-led coalition and Iraqi forces have routinely taken out VBIEDs before drivers could reach their mark. Not all “martyrs” are truly willing recruits. For instance, the Islamic State’s figures include numerous children who were pressed into service by Baghdadi’s goons.

Still, even taking into account these caveats, it is reasonable to conclude that the number of people willing to die for the sake of the so-called caliphate is disturbingly high – much higher than the number of willing martyrs in 2001 or even much more recently. Even though most of these people have been deployed in war zones, it is possible that more will be used outside of Iraq and Syria if they survive the fight and are able to travel to other countries. The Islamic State has already had some success in instigating would-be recruits to die for its cause in the West after they failed to emigrate to the lands of the caliphate. It is certainly possible that more will be sent into Europe or the U.S. in the future.

Children used in suicide attacks, executions and other operations. The Islamic State has a robust program, named “Cubs of the Caliphate,” for indoctrinating children. It is one of the most disturbing aspects of the organization’s operations. Not only does the Islamic State’s propaganda frequently feature children attending classes, its videos have proudly displayed the jihadists’ use of children as executioners.

Earlier this month, for instance, the group’s Wilayah Jazirah disseminated a video entitled, “They Left Their Beds Empty.” Four children are shown beheading Islamic State captives. The same production is laced with footage of the terrorists responsible for the November 2015 Paris attacks, as well as other plots in Europe. Indeed, the children are made to reenact some of the same execution scenes that the Paris attackers carried out before being deployed. The Islamic State’s message is clear: A new generation of jihadists is being raised to replace those who have fallen, including those who have already struck inside Europe.

The “Cubs of the Caliphate” program is not confined to Iraq and Syria, but also operates in Afghanistan and elsewhere. This means that numerous children who have been indoctrinated in the Islamic State’s ways will pose a disturbing challenge for authorities going forward. As I noted above, some have already been used in “martyrdom operations” in Iraq and Syria. It is possible that others could be used in a similar fashion outside of the group’s battlefields, in Europe or the U.S. One purpose behind making children or adults commit heinous acts is to shock their conscience into thinking there is no way back, that they have crossed a threshold and there is no return. There are no easy answers for how to best deal with this problem.

Diversity of terrorist plots. There are legitimate concerns about the possibility of well-trained fighters leaving Iraq and Syria for the West now that the Islamic State is losing its grip on some of its most important locales. We saw the damage that a team of Islamic State operatives can do in November 2015, when multiple locations in Paris were assaulted. Trained operatives have had a hand in other plots as well. This concern was succinctly expressed by EUROPOL in a recent report. “The number of returnees is expected to rise, if IS [Islamic State], as seems likely, is defeated militarily or collapses. An increasing number of returnees will likely strengthen domestic jihadist movements and consequently magnify the threat they pose to the EU.” While a true military defeat will be elusive, the central point stated here has merit, even though the number of arrests of returnees across Europe has recently declined. According to EUROPOL, “[a]rrests for travelling to conflict zones for terrorist purposes…decreased: from 141 in 2015 to 77 in 2016.” And there was a similar “decrease in numbers of arrests of people returning from the conflict zones in Syria and Iraq: from 41 in 2015 to 22 in 2016.”

However, the overall number of arrests “related to jihadist terrorism” rose from 687 in 2015 to 718 in 2016, meaning that most of these terror-related arrests do not involve returnees.

Still, returnees and the logistical support networks that facilitate travel to Iraq and Syria were prominently represented in court cases tried by EUROPOL member states. “As evidenced in the past couple of years, the majority of the verdicts for jihadist terrorism concerned offences related to the conflict in Syria and Iraq,” EUROPOL reported in its statistical review for 2016. “They involved persons who had prepared to leave for or have returned from the conflict zone, as well as persons who have recruited, indoctrinated, financed or facilitated others to travel to Syria and/or Iraq to join the terrorist groups fighting there.” In addition, “[i]ndividuals and cells preparing attacks in Europe and beyond were also brought before courts.”

These data show that while the threat posed by returnees is real, it is just one part of the overall threat picture. The Islamic State has encouraged supporters in the West to lash out in their home countries instead of traveling abroad, directed plots via “remote-control” guides, and otherwise inspired individuals to act on their own. These tactics often don’t require professional terrorists to be dispatched from abroad. The Islamic State has also lowered the bar for what is considered a successful attack, amplifying concepts first espoused by others, especially al Qaeda. A crude knife or machete attack that kills few people is trumpeted as the work of an Islamic State “soldier” or “fighter.” On Bastille Day in Nice, France last year, an Islamic State supporter killed more than 80 people simply by running them over with a lorry. Other Islamic State supporters have utilized this simple technique, repeatedly advocated by Abu Bakr al Baghdadi’s propagandists, as well.

However, I would urge caution. While the amateurs or individual actors have become more lethal over time, the risk of professionally-trained jihadists carrying out a mass casualty attack remains distinct. On average, the professionals can still do more damage than their amateur counterparts – if they are not stopped beforehand. The threat to aviation demonstrates the point. In October 2015, the Islamic State’s Wilayah Sinai downed a Russian airliner, killing all 224 people on board. Although the jihadists claim to have used a crude improvised explosive device, the plot required that well-placed personnel implant it at an optimal location within the aircraft. U.S. officials are attempting to stop even more sophisticated devices, built by either the Islamic State or al Qaeda, from being placed on board flights bound for Europe or America. Other professionally-planned attacks could involve bombing commuter trains, Mumbai-style sieges, or multi-pronged assaults. Therefore, if the professionals are able to evade security measures, they could easily kill more people than the average amateur.

Counterterrorism services in Europe and the U.S. have stopped a number of professional plots through the years. Some of those foiled in the past year may have been more serious than realized at the time. However, there is a risk that as counterterrorism authorities deal with a large number of individual or amateur plots, the professional terrorists will be able to find another window of opportunity. The various threats posed by the Islamic State have placed great strains on our defenses.

The Islamic State could seek to exploit refugee flows once again. “The influx of refugees and migrants to Europe from existing and new conflict zones is expected to continue,” EUROPOL reported in its review of 2016. The Islamic State “has already exploited the flow of refugees and migrants to send individuals to Europe to commit acts of terrorism, which became evident in the 2015 Paris attacks.” The so-called caliphate and “possibly other jihadist terrorist organizations may continue to do so.” While the overwhelming majority of migrants are seeking to better their lives, some will continue to pose a terrorist threat. European nations are dealing with this, in part, by deploying more “investigators” to “migration hotspots in Greece and soon also to Italy.” These “guest officers” will rotate “at key points on the external borders of the EU to strengthen security checks on the inward flows of migrants, in order to identify suspected terrorists and criminals, establishing a second line of defense.”

This makes it imperative that U.S. authorities share intelligence with their European counterparts and receive information in return to better track potential threats. The U.S. has led efforts to disrupt the Islamic State’s “external attack” arm and probably has the best intelligence available on its activities. But European nations have vital intelligence as well, and only by combining data can officials get a better sense of the overall picture. Recent setbacks with respect to this intelligence sharing, after details of British investigations were leaked in the American press, are troubling. But we can hope that these relationships have been repaired, or will be soon.

It should be noted that would-be jihadists who are already citizens of European countries could have an easier route into the U.S. than migrants fleeing the battlefields. It is much easier for a British citizen to get on a plane headed for the U.S. than for an Islamic State operative posing as a Syrian refugee to enter the U.S. clandestinely through Europe. Given recent events in the UK, and the overall scale of the jihadist threat inside Britain, this makes intelligence sharing on potential terrorists all the more crucial. British officials have said that they are investigating 500 possible plots involving 3,000 people on the “top list” of suspects at any given time. In addition, 20,000 people have been on the counterterrorism radar for one reason or another and are still considered potentially problematic.

Exporting terror know-how. It is possible that more of the Islamic State’s terrorist inventions will be exported from abroad into Europe or the U.S. As the self-declared caliphate sought to defend its lands, it devised all sorts of new means for waging war. It modified drones with small explosives and built its own small arms, rockets, bombs and the like. Al Qaeda first started to publish ideas for backpack bombs and other IEDs in its online manuals. The Islamic State has done this as well, but we shouldn’t be surprised if some of its other inventions migrate out of the war zones. The group could do this by publishing technical details in its propaganda, or in-person, with experienced operatives carrying this knowledge with them.

Thomas Joscelyn is a Senior Fellow at the Foundation for Defense of Democracies and the Senior Editor for FDD's Long War Journal.

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