Understanding Federal Law Enforcement in the United States: Part 2

U.S. Customs and Border Protection

This is the second in a six-part series examining major policing strategies through a research-grounded lens, assessing each strategy against multiple criteria.

A traveler arriving at John F. Kennedy International Airport (JFK) hands over their passport. A rancher in southern Arizona sees agents patrolling the mesquite beyond his fence line. A shipping container at the Port of Los Angeles undergoes imaging scans before its contents reach American consumers. All three encounters involve the same federal agency, but most Americans would be hard-pressed to explain how or why.

U.S. Customs and Border Protection (CBP) is the largest federal law enforcement agency in the United States, with more than 60,000 employees and a budget exceeding $19 billion. It is simultaneously a law enforcement agency, a trade facilitation body, and the federal government’s primary screening operation for people and goods entering the country. Understanding how one agency came to hold all of these responsibilities—and what authorities it exercises in each role—is essential context for the policy debates that surround it.

Creation and Legislative Origins

Prior to Sept. 11, 2001, the functions CBP now performs were scattered across three departments:

• The U.S. Customs Service sat within the Treasury Department, tracing its origins to the Fifth Act of the First Congress in 1789.
• Immigration inspection and the U.S. Border Patrol operated under the Immigration and Naturalization Service (INS) within the Department of Justice.
• Agricultural inspections ran through the Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS).

Each had its own chain of command and institutional culture, but no unified border management authority.

The Homeland Security Act of 2002 changed that. The 9/11 Commission found that border security “was not seen as a national security matter” in the decade before the attack. The agencies responsible for customs, immigration, and border inspection operated in separate departments with no shared intelligence or counter-terrorism mission—gaps the hijackers exploited through fraudulent passports, visa application fraud, and watchlist failures. The Commission recommended integrating border security into a comprehensive screening system under a single department so that agencies guarding the border could share intelligence and apply common security standards. Congress responded by directing the consolidation of these functions within the newly created Department of Homeland Security (DHS). 

CBP formally launched on March 1, 2003, integrating the Customs Service, INS immigration inspectors and Border Patrol, and APHIS plant quarantine programs into a single agency. Personnel who had spent careers in agencies with distinct missions (e.g., revenue collection, immigration enforcement, agricultural protection) were now operating under one roof with a new counter-terrorism mandate.

Mission

CBP’s stated mission is to protect the American people, safeguard U.S. borders, and enhance the nation’s economic prosperity. Its 2021–2026 Strategy identifies five “Enduring Mission Priorities”:

• Countering terrorism
• Combating transnational crime
• Securing the border
• Facilitating lawful trade and protecting revenue
• Facilitating lawful travel

That counter-terrorism sits atop CBP’s strategic priorities is notable given that it is also a core mandate of the Federal Bureau of Investigation (FBI). However, the two agencies approach the mission from different directions: CBP focuses on preventing threats from crossing U.S. borders, while the FBI investigates terrorist activity both domestically and internationally.

The dual mandate that distinguishes CBP from other federal agencies is a combination of enforcement and facilitation. On a typical day, CBP processes close to a million travelers at ports of entry while simultaneously conducting cargo screening and border patrol operations. The agency is not solely focused on keeping things out; it is also responsible for keeping commerce and travel moving.

The question of how a border-focused agency operates so far from the border is not new. In 1992, the Border Patrol (then under the INS) was deployed to Los Angeles during the unrest following the Rodney King verdict, and tactical agents conducted the raid to seize Elián González from his relatives’ home in Miami in 2000. The question arose again in 2020, when CBP deployed tactical units to Portland, Oregon, and other American cities during racial justice protests under Operation Diligent Valor—a deployment the DHS inspector general later found agents were unprepared for, with only 7 of 63 officers examined having completed riot and crowd control training. More recently, the deployment of CBP personnel to Minneapolis and other American cities as part of expanded federal enforcement operations has raised similar questions about how an agency whose strategic plan and training infrastructure are organized around border security operates in urban environments far from the border. The distance between the agency’s stated mission and its operations is a question that successive administrations have answered differently.

Scale

CBP currently has 69,874 authorized positions, though reports have found the agency has consistently fallen short of staffing targets, with attrition outpacing hiring in recent years. As of mid-2025, CBP employed approximately 19,000 Border Patrol agents; 26,000 CBP officers; and 1,400 Air and Marine operators.

Staffed primarily by those CBP officers, the Office of Field Operations (OFO) is the component most travelers encounter. OFO oversees 328 ports of entry and maintains a presence at more than 70 international locations across over 40 countries. CBP also stations officers at 15 preclearance locations in six countries, where travelers complete U.S. customs and immigration processing before boarding their U.S.-bound flights. CBP precleared more than 22 million travelers through these facilities in 2024 alone.

Operating between ports of entry, CBP Border Patrol is organized into 20 sector offices patrolling over 6,000 miles of land border with Canada and Mexico. Air and Marine Operations (AMO) adds an aerial and maritime dimension with approximately 240 aircraft and 300 marine vessels.

Jurisdiction

CBP derives its law enforcement authority from two principal statutory sources within the U.S. Code: Title 8 (immigration law) and Title 19 (customs law). How those authorities apply depends on where an encounter takes place.

At ports of entry, CBP officers exercise inspection authority under the “border search exception” to the Fourth Amendment. The legal rationale is straightforward: The government has a sovereign interest in controlling what and who enters the country, and courts have long held that this interest justifies searches at the border that would require a warrant in other settings. In practice, this means officers may conduct routine searches of people and goods entering the country without a warrant, probable cause, or reasonable suspicion. This exception applies at the physical border and at its “functional equivalent,” which includes international airports like JFK.

Away from ports of entry, CBP’s authorities are broader than most realize but more constrained than at the border itself. Under the Immigration and Nationality Act (INA) Section 287(a)(3) and its implementing regulation (Title 8, Part 287), Border Patrol agents may board and search buses, trains, and vehicles without a warrant within what the regulation defines as 100 air miles from any U.S. border, including coastlines. That zone encompasses roughly two-thirds of the U.S. population, including cities like New York, Chicago, and Houston. Under the same statute, agents may access private land (excluding dwellings) within 25 miles of an external boundary.

However, the 100-mile zone does not mark the outer limit of all CBP authority. The INA classifies both CBP and ICE agents as “immigration officers” with certain nationwide enforcement authorities. These include the power to interrogate any person they believe may be an immigrant about their right to be in the United States and to make warrantless arrests when they have reason to believe a person is unlawfully present and likely to escape before a warrant can be obtained. What changes outside the 100-mile zone is the scope of warrantless search authority—agents cannot set up fixed checkpoints or board buses and trains without a warrant beyond that boundary.

Authorities are not applied uniformly throughout the 100-mile zone. The Supreme Court has held that agents may briefly stop vehicles at fixed interior checkpoints to inquire about immigration status without individualized suspicion. Away from checkpoints, roving patrols require reasonable suspicion—specific, articulable facts beyond a mere hunch—for a stop and probable cause or consent for a search. What constitutes reasonable suspicion in practice and what role factors like race, language, and location might play in establishing it remains an active and contested area of law.

How aggressively these authorities are applied in any given area depends on several factors weighed by courts and the agency itself, including how close the encounter is to the actual border, how densely populated the area is, and whether the terrain or transportation routes in question are commonly associated with illegal crossings. An agent stopping a vehicle on a remote highway five miles from the Mexican border operates in a very different legal and operational context than an agent questioning someone at a bus stop in a major metropolitan area 90 miles from the nearest coastline, even though both encounters technically fall within the same 100-mile zone.

Hiring and Training

CBP maintains separate hiring pipelines for CBP officers, Border Patrol agents, and AMO agents, though all share a common baseline. All frontline law enforcement applicants must be U.S. citizens and must pass a background investigation, polygraph examination, medical evaluation, and physical fitness test. Applicants must apply before their 40th birthday—a temporary increase from the standard DHS maximum entry age of 37 adopted to widen the applicant pool amid persistent staffing shortfalls.

Training varies by component. CBP officer candidates attend the Field Operations Academy at the Federal Law Enforcement Training Center (FLETC) in Glynco, Georgia, for an 89-day program covering immigration and trade law, anti-terrorism protocols, search procedures, interviewing techniques, firearms, and officer response tactics. Trainees take a Spanish comprehension assessment, and those who do not demonstrate sufficient proficiency receive additional language instruction. Border Patrol agents train at the Border Patrol Academy in Artesia, New Mexico, for approximately 15 to 19 weeks depending on their need for Spanish language training. AMO agents also train at FLETC, following a curriculum specific to aviation and maritime law enforcement.

Use-of-force policy is a subject of particular public interest. CBP’s publicly available Use of Force Policy governs all three operational components. The policy applies the Graham v. Connor (1989) reasonableness standard, meaning officers are trained to use only the level of force a reasonable officer would consider necessary under the same circumstances. The policy also instructs officers and agents to use de-escalation tactics when feasible and safe. CBP requires all officers to demonstrate firearms proficiency at least twice per year, while Border Patrol and AMO agents must do so quarterly. All CBP personnel receive quarterly use-of-force training that covers firearms, less-lethal devices, and force policy, with annual recertification required for specific less-lethal devices. Simulator training is required annually at CBP’s Advance Training Center in Harpers Ferry, West Virginia. A National Use of Force Review Board reviews significant use-of-force incidents and issues recommendations on policy, training, tactics, and equipment.

Looking Ahead

The next installment examines U.S. Immigration and Customs Enforcement (ICE), the other DHS agency created as part of the 2003 reorganization. Where CBP’s jurisdiction is anchored at and near the border, ICE’s stated mission centers on enforcement in the interior of the country and on criminal investigations involving cross-border violations. While the two agencies share a legislative origin and parent department, their operational footprints—and the public debates surrounding them—differ in several key ways.

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Next in this series: Part 3—U.S. Immigration and Customs Enforcement