The Migration-Terrorism Nexus: Evaluating the Terrorist Threat at the U.S. Southern Border

Executive Summary

The nexus between migration and terrorism has been a focal point in the national security debate, particularly concerning the U.S. southern border. While critics argue that the threat of terrorism through illegal border crossings is exaggerated, a deeper look at the migration-terrorism link in Europe between 2014 and 2018 tells a different story. The evidence from Europe, combined with emerging risks at the U.S.-Mexico border, suggests that the terrorist threat is more significant than initially perceived. This report takes a comprehensive look at how terrorist organizations, including ISIS and al-Qaeda, have historically exploited migration systems, the current state of U.S. border security, and the potential vulnerabilities within the U.S. asylum process.

Analysis

The Argument Against a Terrorist Threat at the Southern Border

A frequently cited position in the debate about border security is that terrorism is not a major issue at the U.S. southern border. Proponents of this view point to U.S. Customs and Border Protection (CBP) data showing that in fiscal year 2021, only a small number of migrants apprehended at the border were flagged as known or suspected terrorists (KSTs). For instance, fewer than 20 individuals from the Terrorist Screening Database (TSDB) were encountered at the southern border in 2021, out of the over 2 million total migrant encounters.

This narrative argues that the overwhelming majority of migrants crossing the southern border are seeking refuge from economic hardship or violence in Central and South America, rather than attempting to engage in terrorist activities. Additionally, supporters of this stance highlight that U.S. border agencies have implemented advanced vetting procedures that minimize the risk of terrorist infiltration.

European Migration Crisis: A Different Picture Emerges

While the U.S. may not have yet experienced a significant terrorism issue at its southern border, the European experience between 2014 and 2018 provides a cautionary tale. During this period, over 104 Islamist extremists entered Europe disguised as refugees or asylum seekers, exploiting the large waves of migration from conflict zones such as Syria, Iraq, and Afghanistan.. These extremists played key roles in devastating terror attacks across Europe, including the Paris attacks in November 2015 and the Brussels bombings in 2016.

In the Paris attacks, two of the perpetrators used falsified Syrian passports to enter Europe, blending in with legitimate refugees. They crossed multiple European borders through Greece, taking advantage of overwhelmed border security systems. European governments, struggling to manage the sheer volume of refugees, were unable to conduct thorough background checks on everyone, creating a window of opportunity for terrorist infiltration.

Further investigations revealed that many of the terrorists who committed these attacks had spent months, if not years, in European countries after entering as asylum seekers. This extended period of legal residence allowed them to plan and coordinate attacks with impunity. For instance, the Syrian asylum seeker behind the Ansbach bombing in Germany in 2016 had spent significant time in Europe under the guise of seeking protection.

The Threat to the U.S. Southern Border: Emerging Risks

Though the scale of migration at the U.S. southern border differs from Europe’s 2014-2018 crisis, similar vulnerabilities exist. A major concern at the U.S.-Mexico border involves “special interest aliens” (SIAs), which are migrants from countries with significant terrorist activity, such as Somalia, Yemen, Syria, and Iran. Between 2019 and 2021, the number of SIAs apprehended at the U.S. southern border increased steadily, raising concerns about potential terrorist infiltration.

The same smuggling networks that facilitate the movement of drugs, weapons, and people across the U.S.-Mexico border could potentially be used by terrorist organizations to move operatives into the U.S. These networks, often run by transnational criminal organizations (TCOs), have developed sophisticated methods to bypass U.S. security measures. The concern is that terrorists, much like they did in Europe, could exploit these routes to blend in with larger groups of migrants.

One notable example is the Duka brothers, who crossed the southern border illegally as children and later became involved in a plot to attack the U.S. military base at Fort Dix. While this case is from the mid-2000s, it illustrates how undetected migrants can, over time, engage in terrorist activities.

Exploitation of the U.S. Asylum System: A Growing Concern

The European experience highlights how terrorists can exploit asylum systems, and the U.S. asylum process shares some of the same vulnerabilities. Migrants who cross the U.S. border and apply for asylum are allowed to remain in the U.S. while their cases are adjudicated, which can take months or even years. This extended period of legal residence creates an opportunity for individuals with malicious intent to embed themselves in American society.

One of the key challenges for U.S. authorities is the backlog of asylum cases, which reached over 1.6 million cases by the end of 2021. This backlog not only delays legitimate asylum claims but also increases the risk that terrorists could abuse the system to remain undetected.

Additionally, the U.S. relies heavily on the Terrorism Screening Database (TSDB) to flag individuals who may pose a national security threat. While this system has helped identify some threats, it is not foolproof. False positives, incomplete data, and the possibility of missing individuals not yet flagged by intelligence agencies mean that some dangerous actors could still slip through the cracks. In some cases, individuals flagged by the TSDB were later cleared, but their initial flagging underscores the inherent risks in the screening process.

Comparing U.S. and European Responses: Key Differences and Similarities

The U.S. has learned from Europe’s mistakes and has implemented more stringent vetting procedures at its borders. Advanced biometric screening, intelligence-sharing agreements with foreign governments, and closer cooperation with Mexico on border enforcement have significantly improved U.S. border security. However, the sheer volume of encounters at the southern border—over 2.4 million in 2021—creates challenges similar to those faced by Europe during its migration crisis.

In Europe, overwhelmed border systems and a lack of coordination between countries allowed terrorists to move freely. The U.S. faces a similar challenge, as transnational criminal organizations have the resources and connections to exploit gaps in border enforcement. Given the complex nature of U.S.-Mexico border dynamics, the U.S. must remain vigilant to prevent a similar scenario where overwhelmed systems lead to security lapses.

Calls for Reform: Strengthening Border Security and Asylum Systems

The report calls for reforms to strengthen U.S. border security and asylum systems to mitigate the risk of terrorist infiltration. First, the U.S. must streamline its asylum process to reduce the backlog of cases and minimize the window of opportunity for potential bad actors. Faster processing times, combined with enhanced background checks for individuals from high-risk countries, could help prevent exploitation of the system.

Secondly, the U.S. should continue to enhance intelligence-sharing efforts with countries in the Middle East and Africa, where terrorist organizations are most active. By improving information flow between U.S. authorities and foreign governments, the U.S. can more effectively screen migrants before they arrive at the border.

Finally, the report recommends that U.S. law enforcement and intelligence agencies remain focused on disrupting transnational criminal organizations that facilitate the smuggling of people across the border. These networks represent one of the most significant vulnerabilities for U.S. border security and must be a top priority in counterterrorism efforts.

Final Thoughts

The data from Europe’s migration crisis between 2014 and 2018 provides a stark warning to the U.S. While the terrorist threat at the southern border may not yet be as pronounced, the risk is real and growing. The increasing presence of special interest aliens, coupled with the potential for exploitation of U.S. asylum systems, highlights the need for stronger border security and more rigorous screening processes. The lessons learned from Europe must inform U.S. policy to prevent terrorist organizations from using migration as a tool for infiltration.