How the U.S. Patrols Its Borders

Introduction

Safeguarding the southern U.S. border, primarily the responsibility of the Department of Homeland Security (DHS), remains a contentious issue as an increasing number of migrants from Asia, Central America, and elsewhere seek to enter the United States via Mexico. President Donald Trump and Democratic lawmakers battled over funding for a U.S.-Mexico border wall, leading to a government shutdown, a presidential emergency declaration, and the deployment of thousands of National Guard and active-duty troops to the border.

Early in his administration, President Joe Biden reversed many Trump-era decisions, including halting construction of the border wall, easing some restrictions on asylum seekers, and pursuing regional diplomacy to target the root causes of irregular migration. However, a continuous flow of migrants arriving at the border is overwhelming the U.S. immigration system and testing federal enforcement capabilities, prompting the administration to resume some construction of the border wall and tighten access to asylum.

What’s happening at the southern U.S. border?

The U.S. immigration system has come under increasing strain in the past decade. After the number of migrant arrivals plunged in 2020 due to the COVID-19 pandemic, illegal border crossings subsequently soared to record highs. In fiscal year 2023 (FY 2023), U.S. immigration authorities apprehended close to 2.5 million people at the U.S.-Mexico border, the highest number ever recorded. As of mid-2024, that number had already surpassed 1.3 million, with a fifth of all migrants coming from the so-called Northern Triangle countries of El Salvador, Guatemala, and Honduras. Other major countries of origin include Colombia, Ecuador, Haiti, and Venezuela.

However, between December 2023 and April 2024, illegal border crossings dropped by some 50 percent. Secretary of Homeland Security Alejandro Mayorkas credited the decrease to various U.S. efforts, including stronger border enforcement and the expansion of legal immigration pathways. Other experts also point to Mexican authorities’ increased efforts to slow U.S.-bound migration and rising deportations. 

Where are most border crossings taking place?

The southern U.S. border, stretching nearly two thousand miles from southern California to the southern tip of Texas at the Gulf of Mexico, has long been the area of highest concern for Border Patrol agents. Of the nine border sectors spread across Arizona, California, New Mexico, and Texas, the greatest number of apprehensions since 2020 have occurred along the easternmost part of the border, called the Rio Grande Valley Sector, in Texas. This is followed by Del Rio, in southwestern Texas, which previously experienced only modest levels of migration.

The types of people arriving at the southern border have varied over time. For much of the 1990s and 2000s, they were largely from Mexico and often adults in search of work. Although migration from Mexico fell sharply beginning in the mid-2000s, it continues to be the primary country of origin for entrants. Meanwhile, the number of migrants from other regions, including Asia and Central and South America, has risen in recent years.

Who is responsible for U.S. border security?

Securing the borders primarily falls to U.S. Customs and Border Protection (CBP), a branch of DHS. Alongside agencies such as the Transportation Security Administration and Drug Enforcement Administration (DEA), CBP is responsible for overseeing and enforcing laws related to trade and travel in and out of the country. Its duties include preventing criminals, would-be terrorists, and contraband from entry. CBP inspects immigrants and cargo at 328 official ports of entry, patrols thousands of miles of border to the country’s north and south, and helps investigate criminal networks, among other responsibilities [PDF]. Of CBP’s more than sixty thousand employees, some one-third are Border Patrol agents, who exclusively work between ports of entry.

When are National Guard forces deployed to the border?

The National Guard, a reserve military force deployed for a wide range of missions at home and abroad, has been called on by U.S. presidents several times over the past two decades to assist border agents with unauthorized immigration and drug trafficking. National Guard soldiers can be called to action by either a state governor or, in some cases, the president. The George W. Bush administration deployed roughly 6,000 National Guard troops to the border, and the Barack Obama administration sent about 1,200 before trimming down the force.

In 2018, guard members were deployed along the southern border as part of a joint operation with CBP known as Guardian Support. Their mission was to assist border agents with logistics, administrative duties, surveillance, and intelligence analysis, as well as provide aerial and mechanical support. By August 2020, the Pentagon had sent more than 2,500 National Guard members [PDF] to aid CBP in the border states of Arizona, California, New Mexico, and Texas. The Trump administration kept National Guard troops there through 2020, even as apprehensions of migrants plummeted and other National Guard personnel were deployed to assist with the pandemic response. In mid-2021, the Biden administration announced that as many as three thousand military personnel would assist CBP and DHS until September 2022. 

Since 2021, Texas Governor Greg Abbott has implemented Operation Lone Star, a $4 billion border enforcement program that aims to curb illegal border crossings with the help of the Texas National Guard and state troopers. Part of the plan includes deploying floating barriers in the Rio Grande to dissuade migrants from crossing. It also called for the installation of razor wire along the Texas-Mexico border, a move that the Supreme Court later ruled against. Operation Lone Star has so far resulted in nearly five hundred thousand apprehensions and more than thirty-eight thousand criminal arrests, while the program’s price tag has exceeded $11 billion. The program has received support from more than a dozen Republican governors, most notably Florida’s Ron DeSantis, who have deployed their states’ National Guard troops and law enforcement officers to the Texas border to assist the operation.

When are active-duty troops deployed there?

It has historically been rare for active-duty U.S. military forces to be sent to the border. In recent decades, soldiers have at times coordinated with border authorities to provide high-tech surveillance and other reconnaissance. 

In late 2018, the Pentagon sent more than five thousand troops to “harden the southern border,” employing them for efforts such as laying razor wire. Critics called the move a political stunt amid a midterm election cycle in which Trump made immigration a central issue. 

Since then, the number of active-duty troops assigned to the southern border has varied. In April 2020, the Pentagon sent roughly 540 additional active-duty personnel to provide surveillance and prevent migrants from entering the United States amid the pandemic. And in May 2023, ahead of the expiration of a pandemic-era health restriction known as Title 42, the Biden administration temporarily deployed an additional 1,500 active-duty troops to the border to relieve pressure on CBP agents.

What are the rules of engagement?

The 1878 Posse Comitatus Act [PDF] limits the U.S. military’s role in enforcing domestic laws, restricting interactions between active-duty troops and migrants at the U.S.-Mexico border. Under these rules, active-duty troops can neither detain and deport unauthorized immigrants nor conduct searches and seizures, though loopholes exist. Like the National Guard, they often provide indirect support, such as conducting aerial surveillance, repairing or reinforcing infrastructure, and performing administrative duties. Unlike the National Guard and CBP, however, active-duty personnel at the border do not carry loaded weapons. 

Armed officials are generally constrained from using deadly force. Under CBP policy [PDF], agents are allowed to use force considered “objectively reasonable and necessary” to gain control of a situation, taking into consideration whether a person poses a security threat or is resisting arrest; excessive force is prohibited. An agent may use deadly force only in a case of imminent danger of death or serious injury. In November 2018, Trump also allowed active-duty troops to conduct crowd control and temporary searches and seizures to assist CBP agents. 

CBP personnel face hundreds of assaults each year. In FY 2023, nearly five hundred officers and agents were attacked while on duty at the southern border, and close to two hundred such incidents have already occurred in the first seven months of FY 2024. The annual number of incidents involving use of force by CBP personnel rose steadily between 2017 and 2021, though it has since dropped; 304 people—both citizens and noncitizens—have been reported killed in confrontations with border agents since 2010.

Is there a threat to U.S. national security?

The Trump administration repeatedly framed border enforcement as a national security priority. It warned of Central American gang members and would-be South Asian and Middle Eastern terrorists joining caravans of migrants to infiltrate the United States. In response to growing migration, Trump declared a national emergency in 2019—which he extended in 2020—that allowed him to redirect some $10 billion from the military budget to fund construction of a wall along the U.S.-Mexico border, which he argued would keep out criminals and halt the flow of illegal drugs. However, while DHS later reported steep drops in apprehensions in areas where border wall sections were added, experts say migrants have long bypassed such barriers.

Many Republicans continue to press Biden to remedy what they say is an ongoing failure to secure the border and safeguard U.S. national security, particularly since border crossings reached a record high in 2023. Experts and lawmakers are also increasingly concerned about the ties between rising immigration and the spread of illegal narcotics, such as the synthetic opioid fentanyl—part of the drug’s supply chain runs through Mexico.

How did Trump change the asylum process?

As a signatory to the 1951 UN Refugee Convention and its 1967 Protocol, the United States has committed to providing refuge to people with a “well-founded fear of being persecuted for reasons of race, religion, nationality, membership of a particular social group or political opinion.” Applicants must demonstrate a credible fear that they would be killed or tortured if returned to their home country. The U.S. Immigration and Nationality Act makes asylum available to those already living in the United States as well as those who arrive at an official port of entry along its borders.

However, Trump denigrated the legal right to seek asylum as a “loophole” in immigration policy, subject to fraud and abuse. His administration pursued policies to block or otherwise discourage asylum seekers from coming to the United States.

Zero tolerance. With long waits at ports of entry driving more asylum seekers to cross at unauthorized points, the Trump administration implemented a blanket zero-tolerance policy intended to increase prosecutions of undocumented migrants who crossed the border illegally, including asylum seekers. (Such prosecutions were relatively infrequent [PDF] under Presidents Bush and Obama, but reached a record level of more than one hundred thousand in 2019.) The government also used the policy to separate children from their parents and detain minors; although Trump signed an executive order in 2018 to end family separations, they continued. The administration also sought to narrow the criteria for asylum [PDF] and deny migrants the right to seek asylum outside ports of entry, but federal courts blocked both of these efforts.

Migrant Protection Protocols. In 2019, a new policy called the Migrant Protection Protocols (MPP), also known as the “Remain in Mexico” program, began requiring migrants to stay in Mexico while U.S. courts processed their asylum claims. The Mexican government agreed to offer them visas and work permits while they waited. Some migrants applied for asylum in Mexico, but they frequently faced unsafe conditions, and the country’s bureaucracy was stretched beyond its capacity to process claims.

Pandemic restrictions. Claiming asylum became even more difficult during the pandemic after the Trump administration invoked Title 42; between 2020 and 2021, the policy was used to deport more than 1.2 million migrants. The approval rate for asylum seekers in 2023 was about 14 percent [PDF], and research has shown that the chances of winning asylum increase fivefold when migrants have legal representation, which is not often the case. A growing backlog in the immigration courts—more than 3.5 million cases as of April 2024—has meant long waits for claims to be heard; still, most asylum seekers appear for their court hearings. Many who lose their cases become undocumented, though in some instances they can appeal the decision.

How is Biden responding?

Biden has dismantled several Trump-era policies while preserving others. He initially suspended federal construction of the southern border wall before moving forward with plans to build additional sections, and he has rescinded Trump’s national emergency declaration. Biden’s administration also officially ended the zero-tolerance policy and the controversial “Remain in Mexico” program after facing legal difficulties. Ahead of the expiration of Title 42 in May 2023, the administration implemented a restrictive new policy that allows the government to deny asylum on certain conditions, though the policy faced legal challenges before an appeals court allowed it to remain in effect. Meanwhile, the administration reopened temporary facilities to house the swelling number of unaccompanied child migrants, who continue to be allowed to stay in the United States. 

At the same time, to incentivize legal migration, the administration has expanded legal pathways for migrants to apply for asylum. These have included creating humanitarian parole programs for migrants from certain countries, including Afghanistan and Ukraine; opening new screening centers in several Latin American countries, such as Colombia and Guatemala; and building upon migration-related pledges made at the 2022 Summit of the Americas. 

Still, the administration continues to face criticism from some lawmakers, who argue the situation has become the “worst border crisis in U.S. history.” As the issue takes center stage in the 2024 presidential campaign, Biden has embraced more-restrictive border measures aimed at curbing migrant arrivals. These include fast-tracked asylum screenings and the implementation of a controversial new policy that temporarily blocks people who illegally cross the U.S.-Mexico border from seeking asylum once the number of daily crossings reaches a certain threshold.