Migration and Terrorism: The United States Can Learn from Europe’s Mistakes

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When asked what kept him up at night in September 2018, Kevin McAleenan, then commissioner of U.S. Customs and Border Protection and now acting secretary of the Department of Homeland Security, replied “I’m concerned about potential terrorism threats attempting entry in the regional migration flow toward the U.S. southern border.” The fear that terrorists might try to infiltrate the United States’ southern border — whether by posing as asylum-seekers or by paying smugglers to sneak in undetected — is hardly new. The vulnerability of the border with Mexico to possible exploitation by terrorists has preoccupied law enforcement officials and others since at least 2002. Nevertheless, the issue has risen to prominence once again, as the Trump administration has sought to justify a range of tougher immigration measures — including a travel ban for select countries, separation and detention of migrant families, and the building of a multibillion dollar wall along the Mexican border. The nature and extent of the threat, and whether the measures in question are necessary and proportionate, have been hotly contested, to say the least. In the meantime, a similar debate has unfolded on the other side of the Atlantic. However, a key difference is that it has now been clearly demonstrated that dozens of terrorists jumped at the opportunity to infiltrate recent irregular migration routes to Europe, directly resulting in numerous, bloody attacks — most notably the marauding jihadist assault on Paris in November 2015. We now also know more about the specific vulnerabilities terrorists were able to exploit, and the ways in which they have been detected. The United States can learn from this experience.

To begin with, we must look at the scale of migration flows and the capacity of receiving states to properly register and screen the incoming migrants. During the height of the crisis in Europe in 2015, more than a million migrants were recorded arriving by way of the Mediterranean Sea — an average of nearly 3,000 people per day. On two consecutive days in October, the number of arrivals exceeded 10,000. Frontline European states simply did not have the capacity to cope. Furthermore, the dysfunctional Dublin Agreement — which dictates that asylum claims must be processed in the first E.U. country in which migrants arrive — effectively created incentives for frontline European states not to register migrants because doing so would mean they would ultimately bear the burden of responsibility. Because many migrants also refused to cooperate, the authorities in Greece and Italy failed to register a significant proportion of new arrivals. Tens of thousands of people were able to enter Europe without being fingerprinted or checked against law enforcement databases. Foreign nationals who had never set foot in Europe before would be unlikely to be registered in European databases in any case, and for those coming from conflict zones — in particular Syria, which contributed the bulk of new arrivals — there were no viable opportunities for cooperation with the countries of origin. This combination of factors meant that during 2015 alone, more than 70 jihadist terrorists that we know of were able to infiltrate European states with relative ease.

The situation in the United States is clearly quite different. The last time the number of migrants apprehended at the southwestern border topped a million was back in 2006, and it has remained at less than half that since 2010. In Fiscal Year 2018, just under 400,000 migrants were apprehended, and there were perhaps 70,000 undetected unlawful entries. On the one hand, this is considerably fewer people than entered Europe in 2015, which was the year that most terrorists were able to infiltrate. On the other hand, these numbers are not insignificant. Moreover, following a surge in arrivals in 2019, McAleenan, (then still commissioner of U.S. Customs and Border Protection), announced, “The system is well beyond capacity, and remains at the breaking point.”

Although this is concerning, there are two critical differences compared to what happened in Europe. First is the fact that most of the people traveling to America’s southern border do not come from countries with significant terrorism problems. This is important, because research has shown that “migrants stemming from terrorist-prone states … are indeed an important vehicle through which terrorism does diffuse.” In U.S. government terminology, “terrorist-prone states” are referred to as countries of “special interest” and migrants coming from such places as “special interest aliens.” Although the terms are only loosely defined, it appears to refer to any country where terrorists are known or suspected to have a significant presence and may enjoy a degree of safe haven. There is no definitive list, but as many as 63 countries have been designated as being of special interest based on these grounds. Crucially, special interest aliens make up only a fraction of migrants who travel by way of Mexico. According to Cato Institute researchers David Bier and Alex Nowrasteh, from 2007 to 2017, U.S. Border Patrol apprehended a total of 45,006 individuals from “special interest” countries. During 2016, when the highest number of special interest aliens entering the United States was recorded, this worked out to about two percent of all apprehensions. By comparison, more than 80 percent of migrant arrivals to Europe in 2015 would be classed as special interest aliens, fewer than one percent of whom were terrorists.

The second key difference between the United States and Europe is what happens when irregular migrants arrive at the border. In the United States, so-called “catch and release” policies do mean that significant numbers of those who claim asylum are allowed into the country while their claim is being processed — including women and children and those deemed to pose little threat to security or risk of absconding. Of course, some of these individuals abscond anyway. However, asylum applicants are also interviewed, fingerprinted, and evidently checked against the Terrorist Screening Database, which includes more than a million known or suspected terrorists. Furthermore, adult males are generally detained while their case is being processed, especially since a “zero tolerance” policy to illegal border crossing was announced in April 2018. This would be especially likely for special interest aliens.

By comparison, as we have already seen, during 2015 many thousands of migrants were able to enter Europe without being fingerprinted or checked against databases, and they often had no documents to establish their true identity. Transit countries then actively facilitated their onward journeys north, while countries of destination found themselves unable to cope with the tidal wave of asylum applications. For a period of time in Germany, Syrians, Iraqis, and Eritreans were able to claim asylum by simply filling in a questionnaire, with no requirement for face-to-face interviews. Although Customs and Border Protection is struggling to deal with migration at the southern border — and this in itself might create vulnerabilities that criminals and terrorists could potentially exploit — the United States has not experienced anything near the same influx of special interest aliens, nor has it suffered a comparable breakdown in either external or internal security.

At least partly because of this, fewer terrorists appear to have been able to infiltrate the United States as compared to Europe. According to Todd Bensman of the Center for Immigration Studies (citing intelligence community sources), at least 100 migrants from “countries of interest,” encountered between 2012 and 2017 at or en route to the southern border were matches on U.S. terrorism watch lists. It is worth bearing in mind, however, that a watch list “hit” does not automatically confirm that the person is actually a terrorist, and so it is difficult to know precisely what to make of this without more details. Using open sources, Bensman identifies a total of 15 known or suspected terrorists of any ideological persuasion who were detained at or en route to the U.S.-Mexico border, or who successfully crossed it, since 2001. Several of these examples are still questionable; none of them conducted attacks in the United States (though one did so in Canada), and only two were charged with terrorism offenses. Three additional individuals who illegally crossed from Mexico into the United States were convicted of planning an attack on Fort Dix, New Jersey, in 2008 — but they had arrived as children traveling with their parents in 1984. This does not mean that the threat is nonexistent. However, confirmed cases of terrorist infiltration of the southern border are few and far between, and we are left with a lingering sense of uncertainty.



In contrast, I have identified more than 140 jihadist “terrorist asylum-seekers” (terrorists who traveled as irregular migrants and/or claimed asylum), who traveled to or within Europe from 2011 to 2018. They have been responsible for at least 13 attacks in seven European countries, resulting in more than 180 fatalities; two dozen additional attack plans have been thwarted. Others have engaged in recruitment, distribution of propaganda, fundraising, and facilitation. By far the most effective terrorists to infiltrate recent migrant flows to Europe have been long-term European residents and citizens, who in most cases had already been flagged as suspected terrorists on account of traveling to Syria and were therefore unable to return home using conventional means. However, the bulk of “terrorist asylum-seekers” have been Syrians, Iraqis, and North Africans, most of whom were members of foreign terrorist organizations (chief among them the Islamic State group) before they arrived.

As already noted, it was a near-total breakdown in security measures that enabled this to happen. Since then, Europe has corrected course. Migrant flows are now far more manageable, thanks to oft-maligned deals with Turkey and Libya, and ongoing efforts to build capacity at the external borders. As a result, all newly arriving migrants are now fingerprinted and checked against databases for connections to criminality and terrorism. The databases themselves have also been updated, and law enforcement agencies now have access to Eurodac, which is used to register the incoming migrants. Together with Europol, the European Border and Coast Guard Agency (commonly known as Frontex) has also developed a handbook of “common risk indicators” to assist border guards with identifying potential signs of involvement in terrorism for migrants who are not necessarily registered in any databases. There are also important efforts at the European level to enhance military-to-law enforcement information exchanges and to improve cooperation with numerous source and transit countries in order to gain better intelligence and evidence on foreign terrorists.

Within Europe, there is also closer cooperation between security services and migration agencies, which previously were not involved in counter-terrorism but have a significant contribution to make. Additionally, some law enforcement and intelligence agencies have conducted outreach activities in migrant accommodation centers, where they provide basic training for staff on possible signs of radicalization, among other things. All of these efforts combined have helped reduce the chances that terrorists might infiltrate external borders in the first place, while increasing the likelihood that they will be detected should they succeed. Crucially, however, the single most important source of investigations in this area has been tip-offs from within the migrant community. Securing borders and enhancing both international and domestic cooperation are important, but human intelligence is key.

What are the lessons for the United States? The first is that whatever vulnerabilities still exist at the southern border, U.S. security is already pretty good (especially relative to the scale of the threat). To begin with, the vast majority of special-interest migrants coming to the United States by way of South and Central America — unlike their European-bound counterparts — initially travel by air. Though not impossible to circumvent, this adds an additional layer of security. They must also travel much farther, which necessarily increases the odds of detection. These odds are further tipped in the United States’ favor by the fact that the U.S. military is active in source countries like Syria and Iraq and has long-established, proven mechanisms for sharing battlefield intelligence and evidence with the FBI and Department of Homeland Security. U.S. officials also have strong cooperation with foreign counterparts in transit countries, and any migrants that make it to the U.S. border are detained and subject to screening. Because Customs and Border Protection, U.S. Immigration and Customs Enforcement and U.S. Citizenship and Immigration Services are all part of the Department of Homeland Security and work closely with the FBI (not to mention that they all belong to the same country and speak the same language), there are also likely to be far fewer obstacles to interagency cooperation than in Europe. On top of all this, U.S. law enforcement agencies already invest extensively in cultivating human sources within immigration detention centers and indeed throughout the country.

Given this, there is a fairly convincing argument to be made that — at least as far as potential terrorist infiltration is concerned — the southern border is far less vulnerable than many like to think. That is not to say that there isn’t room for improvement. Since Customs and Border Protection says it is at “breaking point” along the southwest border, appropriate steps should of course be taken to address this. Continued capacity-building efforts and joint investigations with foreign counterparts to disrupt smuggling networks and identify any terrorists before they reach the U.S. border may help to alleviate some of this pressure. More direct efforts might include increases in personnel and other resources to ensure that all newly arriving migrants continue to be properly registered and screened, and that undetected unlawful entries are minimized. However, the second important lesson from the European experience is that the chances of detecting terrorist asylum-seekers appear to be higher within the country, rather than at the external borders. For this reason, it may be more worthwhile to focus on the situation of migrants and asylum-seekers inside the country, and to critically assess related capabilities to detect any potential threat. If events in Europe are anything to go by, human intelligence is likely to be central to these efforts.

In the final analysis, we must not lose sight of the fact that total security against terrorism is impossible. The United States has been tremendously successful in securing the homeland against foreign terrorists since 2001 and in fact most attacks since then have been conducted by long-term residents and citizens, who evidently radicalized at home. Terrorist infiltration of the southern border is certainly possible, and Americans should not ignore this. But the demonstrable threat so far has been small, and it remains relatively unlikely. Looking across the Atlantic, where terrorist infiltration has taken place on a much larger scale and with devastating consequences, Americans should feel reassured that their own borders do not suffer from the same gaping holes in security that terrorists were able to exploit in Europe. Preventing and detecting terrorist infiltration in future will depend upon carefully targeted, intelligence-led policing. Building a wall along the entire nearly 2,000-mile-long border with Mexico — regardless of what it might achieve — would simply not be cost-effective.



Sam Mullins is a professor of counter-terrorism at the George C. Marshall European Center for Security Studies, Germany, and an honorary principal fellow at the University of Wollongong, Australia. He is the author of Jihadist Infiltration of Migrant Flows to Europe: Perpetrators, Modus Operandi and Policy Implications. Views expressed are his own.


Image: U.S. Customs and Border Protection photo by Josh Denmark