From Counterterrorism to Immigration Enforcement: 25 Years On, Post-9/11 U.S. Changes Have Been Repointed

Twenty-five years after the September 11, 2001 terrorist attacks transformed U.S. society and government, many of the cornerstone national security tools deployed to prevent future terrorism have been repurposed by the Trump administration for its far-reaching immigration agenda. The seismic government transformation that occurred post-9/11 included creating the Department of Homeland Security (DHS), enacting the USA Patriot Act, and investing in expansive data-sharing and surveillance technology. The national security lens increasingly applied to the U.S. immigration system after 9/11 has been magnified by the administration’s relentless focus on immigration enforcement and supercharged by the proliferation of artificial intelligence (AI) and the expanded use of surveillance and facial recognition technology.

The administration’s scrutiny of noncitizens, lawfully present and otherwise, based on their perceived ideology and nationality, increased monitoring and surveillance, and heightened ability to connect and analyze vast quantities of data have roots in the post-9/11 enforcement machinery. Modern tech tools have added a new arsenal to the government's ability to identify, target, track, arrest, detain, and quickly deport large numbers of noncitizens. The result is that the Trump administration has blended the domains of counterterrorism and immigration enforcement to create something resembling a domestic intelligence apparatus, with increasing repercussions for U.S. citizens.

Post-9/11, the government went through the largest bureaucratic restructuring since World War II, abolishing the U.S. Immigration and Naturalization Service (INS) and folding its functions into DHS, which brought together 22 federal agencies. Immigration enforcement, which encompasses just a fraction of the department’s mandate, now overshadows all other DHS functions and the budgets of all law enforcement agencies nationwide, with ripple effects across government. This growth in resources and powers has been accompanied by renewed concerns over civil liberties and privacy, many of which took shape in the immediate aftermath of 9/11.

This article examines how the legal and policy shifts of the post-9/11 era have been used for immigration enforcement. It covers the expansion of surveillance, how authorities consider an individual’s ideology in immigration processes, increased funding, and the spillover impacts on U.S. citizens.

"The administration has blended the domains of counterterrorism and immigration enforcement to create something resembling a domestic intelligence apparatus, with increasing repercussions for U.S. citizens."

Intelligence Infrastructure Built and Rebranded

To prevent future terrorist attacks, the government post-9/11 built expansive infrastructure for vetting travelers, data sharing, and surveilling potential threats. Amid concerns about the blind spots between intelligence and law enforcement agencies that could have forewarned of the al Qaeda plot, there was a particular focus on breaking down information and data silos.

Among other programs, this resulted in the creation of the National Security Entry-Exit Registration System (NSEERS), which required noncitizen males 16 and older from 25 countries (24 of which were Muslim-majority) to submit biometrics upon arrival in the United States and meet with immigration officials in person during their stay. For those already in the country, in-person registration was required. NSEERS was eventually dismantled and terminated by 2011, by which point it had become supplementary to the U.S. Visitor and Immigrant Status Indicator Technology (US-VISIT), created in 2004, which gathered biometrics on all foreigners entering the country.

Separately, in the wake of 9/11, the federal government ramped up use of the 287(g) program that allows state and local law enforcement agencies to cooperate and share data with U.S. Immigration and Customs Enforcement (ICE). Although the 287(g) program was created by a 1996 law, the first agreement was not signed until 2002, with the state of Florida.1

Among the most sweeping legal changes was enactment of the USA Patriot Act, which provided tools to identify noncitizens posing a potential terrorist threat, expanded surveillance and information collection, and hardened immigration and criminal law enforcement powers.2 It sought to increase information sharing among agencies, merging federal intelligence and criminal databases. It re-envisioned the Watergate-era Foreign Intelligence Surveillance Act (FISA) to blur the line between gathering intelligence and conducting criminal investigations.3 The law also allowed for increased use of wiretaps and expanded the government’s access to personal records.

Repointing the Surveillance Apparatus for Immigration Enforcement

Despite occasional public opposition, many of these and similar tools have since become normalized. But only under the Trump administration has this expansive data sharing and monitoring been used in service of large-scale deportations. Authorities have combined these legal powers with advanced analytics and AI resources unheard of in the post-9/11 days.

Some of the Trump policy changes adopted a blanket approach, rather than the more targeted focus seen during the post-9/11 period. A February 2025 executive order required registration by certain noncitizens who had not previously submitted information, which DHS estimated could affect as many as 3.2 million people, a policy reminiscent of NSEERS yet vastly larger in scope.4 Increased vetting, including of social media accounts and finances, has similarly applied broadly.5 In other instances, the administration has used national security grounds to target certain groups or nationalities, such as by designating the Venezuelan gang Tren de Aragua a terrorist organization and halting travel to the United States for nationals of 75 countries (this pause was halted by a federal court as of this writing, with further litigation pending).

"Only under the Trump administration has this expansive data sharing and monitoring been used in service of large-scale deportations."

Increased interagency data sharing has been a major focus for the Trump administration. A March 2025 executive order called for “eliminating information silos,”6 which laid the groundwork for transferring unprecedented amounts of sensitive personal information to immigration enforcement officials, including from agencies with no federal immigration enforcement mission such as the Social Security Administration, the Internal Revenue Service (IRS), and the Department of Health and Human Services.7 The order also allowed for the creation of a mega-immigration database, known as ImmigrationOS, pulling in government and private-sector data on individuals to support immigration enforcement.8 Built by Palantir Technologies, a longtime DHS contractor, ImmigrationOS combines data from a variety of sources, creating a system that tracks noncitizens from identification to deportation, monitors self-deportations, and prioritizes targets for enforcement.9

Information sharing between local, state, and federal authorities has increased since President Donald Trump returned to office. A proclamation issued his first day called for state and local assistance in immigration enforcement.10 Under the Trump administration, the number of 287(g) agreements between state and local law enforcement and ICE has ballooned from 135 at the end of 2024 to 2,559 as of September 21, 2026 (see Figure 1).11 Seventy percent of these agreements are of the previously discontinued task force model, which allows local or state officers to perform federal immigration duties; the model had previously been phased out under the Obama administration amid concerns over racial profiling.12

Modern tools have powered the repointing of the government’s surveillance dragnet to immigration enforcement. Harnessing AI, ICE has contracted with private companies to use tools including facial recognition technology. One example is Mobile Fortify, an app that federal agents in the field can use to scan faces and fingerprints and check them against government databases.13 ICE and its contractors rely on a variety of open-source data (often collected by private companies from state agencies or telecom providers) to create expansive platforms such as Palantir’s Enhanced Leads Identification and Targeting for Enforcement (ELITE), which populates a map with noncitizen targets’ locations using their name, most recent address, government “alien registration number” (A-number), and date of birth; it is specifically focused on areas with large immigrant populations.14 Cellphone location data fuels many apps, allowing for near real-time tracking of specific phones and linking phone numbers to individuals’ email addresses, driver’s license information, and addresses, among other personal information.15 Because of the secret nature of many government systems, the full scope of the systems ushered in by these tools is yet to be fully understood.

Immigration Barriers on Ideological Grounds

Notably, the USA Patriot Act also revived the government’s ability to refuse entry or deport someone based on ideological grounds, as previously outlined in the Immigration and Nationality Act (INA) of 1952 (also known as the McCarran-Walter Act) for use against anarchists, communists, and supporters or advocates for totalitarian governments.16 During the Cold War, this power was widely used to deny visas to individuals with political affiliations or public opinions deemed oppositional to the U.S. government, including Chilean poet and politician Pablo Neruda and actor Charlie Chaplin.17

This INA provision had faced criticism that it violated the First Amendment’s guarantee of free speech. In the 1972 Supreme Court case Kleindienst v. Mandel, petitioning academics argued that denying a visa to the Belgian Marxist Ernst Mandel to attend speaking events at U.S. institutions violated the First Amendment by restricting ideas from abroad.18 Though the court agreed that denying a visa to Mandel affected free speech, it upheld the denial because Mandel had violated the terms of a previous visa, thereby leaving open the question of whether denying a visa for ideological reasons violated the First Amendment.19

In 1990, Congress repealed the INA’s authority to exclude a noncitizen for ideological grounds, but, without a firm decision by the Supreme Court, it was quickly resurrected post-9/11. Section 411 of the USA Patriot Act amended the INA to bar from the country:

• Members of groups supporting terrorism in the United States,
• People who use a prominent position to encourage others to support terrorism,
• Anyone the secretary of state or attorney general determines to be involved in an activity contrary to U.S. interests,
• Anyone providing financial support for a terrorist organization, and
• Close family members of anyone who falls under those categories.20

As under the McCarron-Walter Act, speech—not just actions—could be considered grounds for inadmissibility.

Scrutiny Has Become More Expansive

Under the Trump administration, ideological scrutiny has come to play a large part in immigration policy, with a broader focus than what was outlined in McCarron-Walter and the USA Patriot Act. The government’s scrutiny of noncitizens’ ideology has led to high-profile enforcement actions involving individuals such as former Columbia University graduate student Mahmoud Khalil and Tufts University doctoral student Rümeysa Öztürk.

A Day One Trump executive order established guidelines to screen out visa applicants who “espouse hateful ideology” and directed agencies to scrutinize noncitizens—including those already in the United States—to ensure they “do not bear hostile attitudes toward its citizens, culture, government, institutions, or founding principles, and do not advocate for, aid, or support designated foreign terrorists and other threats to our national security.” 21This order laid the groundwork for specific policy guidance such as U.S. Citizenship and Immigration Services (USCIS) directives to consider “anti-Americanism” 22and antisemitism23 in deciding whether to grant legal status and other immigration benefits. These policies leave considerable room for discretion, given that “anti-Americanism” is not specifically defined. Additionally, the State Department directed consular officers to deny visas to individuals who worked as fact-checkers, content moderators, or were otherwise deemed to be engaging in “censorship.”24 The guidance was aimed mostly at applicants for H-1B visas for highly skilled workers at tech companies, many of which routinely moderate online content for abuse, fraud, illegal postings, or other harmful rhetoric.

Whereas in the past the government’s scrutiny of noncitizens’ ideologies relied on ties to known organizations, tips from watchlists, hits on government databases, publicized remarks, or in more extreme cases informants and surveillance, its powers have been supercharged by individuals’ visible presences online, including social media. USCIS collects social media handles for some applications and border officials can request to review an individual’s phone or computer upon arrival. This allows for scrutiny of a wide range of online activity.

This expansive scope became evident during the administration’s targeting of foreign students, especially those publicly critical of Israel’s actions in Gaza, which authorities labeled antisemitic. Several individuals—including Khalil, Öztürk, and Columbia grad student Mohsen Mahdawi—were arrested, detained, and put in deportation proceedings. The administration sought to target them using a rarely used Cold War-era provision of the INA, 237(a)(4)(C)(i), which allows noncitizens to be deported if their “presence and activities in the United States the secretary of state has reasonable ground to believe would have potentially serious adverse foreign policy consequences.”25 In addition to concerns about the circumstances of the arrests and detention, the focus on students’ publications, public speeches, and online posts raised questions about infringements of their First Amendment rights. In the lawsuit AAUP v. Rubio, U.S. District Judge William Young determined that the government’s actions violated the student’s free-speech rights; as of this writing, the case was on appeal to the First U.S. Circuit Court of Appeals.26

Dragnet Ensnares U.S. Citizens

The infrastructure used for targeting, tracking, and arresting immigrants has had spillover effects on U.S. citizens. For example, the Border Patrol uses its vast nationwide network of license plate readers to track a car’s “suspicious” movements, link that data with financial information, and share it with local or state law enforcement.27 Authorities may then pull over the vehicle for a different reason, such as an obstructed license plate. This highly controversial practice, known as predictive policing, has been described as allowing authorities to detain people whom they think may have committed crimes even if there is no evidence of criminal activity.28

Much of the public debate around license plate readers has centered on Flock Safety. The company's cameras capture license plates and analyze vehicles' movement to determine where someone lives, works, or frequents, putting that data up for sale.29 Although ICE does not buy information directly from Flock, it has gained access to the company’s data through its agreements with local authorities.30 Outside the immigration realm, Flock has been at the center of concerns about U.S. citizens’ privacy rights, with dozens of cities—Democratic- and Republican-led alike—terminating contracts with the company,31 although proponents say the technology makes communities safer.

ICE Tracking and Alleged Intimidation

ICE observers—civilian bystanders documenting officers’ activities—have repeatedly had tense interactions with agents. Authorities have photographed observers and their license plates, and the agency has acknowledged that it maintains data—including biometric information—about protesters and others whom it suspects may be interfering with ICE operations, even if they are never arrested.32 In some instances, observers have said they were followed, reported to local police, or visited at home by federal agents.33 One man has claimed his and his wife’s Global Entry status was revoked after recording immigration authorities (it was later reinstated).34

Several of these individuals and others have sued the government, claiming First Amendment violations. For example, the Foundation for Individual Rights and Expression (FIRE) filed suit after federal agents allegedly sought to confront a Rochester, NY resident at his home and at a New York City hotel to warn him that a critical email to then ICE Acting Director Todd Lyons could amount to an illegal threat.35 In another case, Rosado v. Bondi, U.S. District Court Judge Jorge Alonso, in Illinois, ruled the government most likely violated First Amendment rights by pressuring Facebook and Apple to prevent apps tracking ICE activity.36

New and Expanded Funding

The reshaping of the federal government following 9/11 vastly increased funding for immigration enforcement. In fiscal year (FY) 2000, the INS budget was $4.3 billion, only a portion of which was allocated for enforcement, as the agency also was responsible for processing immigration benefits applications. By FY 2006, funding for DHS was $12.5 billion, a tripling of its predecessor’s available resources.

"ICE is now the highest-funded law enforcement agency in the country."

Funding for immigration enforcement has increased virtually every year since (see Figure 2) and further ballooned in FY 2025 with passage of the One Big Beautiful Bill Act (OBBBA) which provides $170 billion over four years for immigration enforcement.37 The budget grew again in FY 2026 through a reconciliation bill allocating another nearly $70 billion for ICE and U.S. Customs and Border Protection (CBP).38 Both packages provide funding through 2029, adding up to nearly $240 billion in immigration enforcement funding over four years. By comparison, the government spent $187 billion total on immigration enforcement during the 26 years from FY 1986 through 2012 (this figure includes the total budget for INS, only a portion of which was devoted to enforcement).39 ICE is now the highest-funded law enforcement agency in the country, surpassing the Federal Bureau of Investigation (FBI) and all other federal law enforcement agencies.

The impacts of this funding remain to be fully felt, although some of it is going to increased detention space, additional border barriers, new technology, and rapid hiring of ICE agents.40 Yet some pitfalls of the rapid speed of spending may already be evident. For instance, ICE decreased mandatory training times to quickly hire new agents, raising concerns about untrained and unvetted agents in the field.41 And although the agency has increased bedspace, many detainees lack access to regular medical care42—including prenatal care for the record number of pregnant women in detention43—among other issues, including recurring complaints of overcrowding and inadequate nutrition.

Funding levels have long driven policy, and the current dynamic is no exception: Flush with cash, immigration enforcement agencies can expand in ways yet to be fully understood.

In Invoking 9/11 Era Policies, Trump Meets Resistance

The impacts of policy choices made in one era can resound in another. The foundational changes made in the aftermath of 9/11 have become the bedrock of the Trump administration’s immigration enforcement agenda in ways that even the authors of those policies could not have envisioned. The Trump administration has invoked these counterterrorism policies, boosted their capabilities with modern tools, and rebranded them to advance its immigration agenda.

As the Trump administration has in some ways been emboldened by the legacy of the 9/11 era, however, it has also been constrained by it. Twenty-five years ago, the judiciary was largely deferential to the executive branch’s actions concerning national security. Even the most liberal federal courts allowed the government to withhold detainees’ names and locations and keep secret evidence in secret proceedings and prolonged detention in immigration cases.44 And while much of the public ultimately turned against the George W. Bush administration amid the war in Iraq, public support immediately post-9/11 was the highest in recent history.45

Now, the Trump administration has met a more skeptical judiciary and public.46 Federal courts have regularly rebuked the administration’s actions on immigration, especially when they have come up against constitutional rights. And although public opinion has generally supported efforts to curb unauthorized immigration and deport criminals, opposition to ICE’s actions have grown, and many states and localities have adopted policies to blunt ICE activity.

The Trump administration’s retooling of post-9/11 national security policies for routine immigration enforcement has upended the lives of hundreds of thousands of individuals, many with deep roots in the United States. The Bush administration’s approach may have been at least initially more palatable because of the real and immediate national security threat of the September 11 terrorist attacks. However, the Trump administration’s repurposing of these national security tools is becoming less popular, showcasing the limits of continued public support for the policies.

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