The Further from 9/11, the Worse Our Judgment about Terrorism Risk

Nineteen foreign-born Islamist terrorists murdered 2,979 innocent people twenty-three years ago today in the deadliest and most destructive terrorist attack in world history. In the aftermath of 9/11, the government and security experts inundated Americans with warnings about impending terrorist attacks, the threat of Al Qaeda, how terrorists were on the cusp of acquiring nuclear weapons, and numerous other predictions that didn’t come to pass.

Since 9/11, foreign-born terrorists have murdered 44 people in attacks on US soil, 37 of them slain by Islamist terrorists. Native-born American terrorists have murdered an additional 73. During that time, the annual chance of being murdered in a foreign-born terrorist attack was about 1 in 165 million per year. Americans were almost 10,000 times less likely to be murdered by a foreign-born terrorist in an attack on US soil than to be murdered in an ordinary homicide. That low level of foreign-born terrorism hasn’t calmed political fears  – it’s just periodically transferred them to different foreign-born subpopulations.

As public concerns about different foreign-born subpopulations change, people attach a greater terrorism risk to those subpopulations. Politicians went from grossly exaggerating the risk of terrorism after 9/11 to quickly concentrating on the threat posed by all foreign-born terrorists like those who attacked that day 23 years ago. Eighteen of the nineteen hijackers entered on tourist visas, the nineteenth on a student visa.

The ongoing Syrian civil war drove the debate over foreign-born terrorism during the 2016 presidential campaign and the early years of the first Trump administration. The changing political debate shifted the focus to refugees, a subset of the foreign-born population, as a major terror threat. That fear prompted President Trump to reduce the size of the American refugee program by almost 90 percent in his first term.

A single Sudanese refugee inspired by anti-white racial animus murdered an American in 2017, after having legally entered the US as a child 21 years earlier. Previously, the last murder by a refugee terrorist in an attack on US soil was committed in 1976 by a Cuban-born anti-communist. There were 15 convictions of refugees for planning terrorist attacks on US-soil from 9/11 through September of 2024, one of them a Syrian refugee who plotted to attack a church in Pittsburgh attended by mostly Nigerian-American congregants. All but one of those 15 was inspired by Islamist ideology.

Then the threat posed by foreign-born refugee terrorists withered. Now, those concerned about terrorism focus on the risk posed by illegal immigrants, yet another subset of the foreign-born population.

Since the end of 2020, US Border Patrol has encountered almost 7.3 million illegal immigrants (technically the number of encounters with illegal immigrants, not the number of different individuals) who crossed the US-Mexico border to work in America’s booming labor market. The public’s perception of immigration and border chaos justifiably increased in response to this surge, but it also created fears of terrorists hidden among them.

The fear appears to be warranted in some cases. From late 2020 through July 2024, Border Patrol apprehended 378 noncitizens along the US-Mexico border who were on the terrorism watchlist  – about 34 times as many as entered in the previous four years. FBI Director Chris Wray has warned about the threat of terrorists crossing the border illegally. Members of Congress are outraged about it and held several hearings on the topic, including one where some members were not pleased by my testimony. However, those numbers and statements by government officials appear to vastly exaggerate the danger.

First, the terrorism watchlists contain millions of people, and almost all of them are not actually terrorists intent on attacking the United States. The government should still block them from entering the country, but it’s telling that not one of the 378 people apprehended has been accused of a domestic terrorist plot, prosecuted for a plot, or, thankfully, actually committed an attack.

Second, the base rate of foreign-born terrorism is low, and the rate of attacks committed by illegal immigrants is lower still. Since 1975, foreign-born terrorists have murdered 3,046 people in attacks on US soil. Zero of those deadly attacks were committed by a terrorist who entered illegally through the US-Mexico border or elsewhere. Nine foreign-born terrorists were apprehended entering the United States illegally during that period. Three of them, the Duka brothers, crossed the US-Mexico border illegally as young children and were arrested for the Fort Dix plot in 2007. As Michael J. Ard and I wrote in a recent piece:

They [the Duka brothers] were arrested after a video clerk saw a VHS recording that the brothers taped of themselves pretending to be terrorists. It was not a serious plot and none of the six others killed or injured anybody in an attack. Past occurrences are no guarantee of future events, of course, but the base rate in this case is zero.

None of the six others successfully committed an attack.

Third, illegal border crossers from Colombia likely dominate those who were apprehended by Border Patrol and who appeared on the terrorism watchlist. Government data on the nationalities of illegal immigrants who are on the watchlist is scarce, and the federal government has refused my FOIA requests asking about them. But leaked data from the first half of 2022 show that 25 of the 27 apprehended were Colombian and likely former members of insurgent groups in that country that have never targeted the US. More broadly, over 92.5 percent of those illegal border crossers whom Border Patrol apprehended were from the Western Hemisphere since late 2020.

Since 9/11, terrorists from our hemisphere have murdered zero people in terrorist attacks on US soil and injured a single person: Paul Pelosi, Nancy Pelosi's husband, who was injured in an attempted kidnapping by Canadian David DePape.

There are so few attacks committed by foreign-born terrorists that some commentators are even resorting to making up terrorist attacks that didn’t happen, turning the arrest of two truck drivers for trespassing at Quantico into a national security scandal. One person familiar with the incident even warned, “The same truck, had it been loaded with explosives, could have been a devastating weapon if it made it close enough to an occupied building.” The drivers not being terrorists, however, raises the question why they would have loaded a truck with explosives in the first place.

Broader public concern about immigration explains the shifting pattern of public concern and political fear focused on the specific foreign sources of terrorism. When politicians and the public were worried about refugees in general, they linked the terrorist threat to refugees. Now that politicians and the public are concerned about the large number of unlawful border crossers over the last several years, they are linking terrorism with illegal immigration.

The public and policymakers are worried about illegal immigration and border chaos in general, so they want to consistently link illegal immigration to the dramatic threat of terrorism. But as public perception of terrorism risk shifts to different foreign-born subpopulations, the terrorism risk posed by each population is smaller than the previous focus.

The risk and harm of terrorism are exaggerated, and the US government has irrationally responded to it by diminishing our civil liberties, starting and losing several foreign wars, restricting migration and travel, and otherwise imposing costs on Americans to a degree grossly disproportionate to the hazard.

Foreign-born terrorists will likely strike again, and an illegal immigrant could commit an attack, as I wrote about here. Still, we should view terrorism as the small and manageable threat that it poses. 9/11 was a devastating terrorist attack, and the government should focus on keeping foreign-born terrorists and other criminals out of the United States. Every person murdered in a terrorist attack is a victim and they and their families deserve to be avenged. But we should not exaggerate the threat of terrorism to dominate the debate over aspects of immigration policy that have little to do with it.