How the U.S. Patrols Its Borders

How the U.S. Patrols Its Borders

As the debate over how to safeguard the U.S. southern border intensifies, President Biden is seeking to reverse much of the Trump administration’s approach.
Unaccompanied children seeking U.S. asylum sit near a Border Patrol vehicle in Penitas, Texas.
Unaccompanied children seeking U.S. asylum sit near a Border Patrol vehicle in Penitas, Texas. Adrees Latif/Reuters
  • U.S. Customs and Border Protection (CBP), along with other agencies, regulates trade and travel at U.S. ports of entry and across the country’s borders.
  • President Trump deployed thousands of National Guard and active-duty military personnel to help secure the border with Mexico and declared a national emergency that unlocked funding for the border wall.
  • President Biden, facing a rise in migrants arriving at the southern border, has reversed Trump-era policies and seeks to fundamentally reform the immigration enforcement system.

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

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Early in his administration, President Joe Biden has begun reversing Trump-era decisions, including halting construction of the wall, easing some restrictions on asylum seekers, and pursuing regional diplomacy to target the causes of migration. However, increasing arrivals at the border are once again testing U.S. enforcement capabilities.

What’s happening at the southern border?

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In early 2021, the Biden administration said it was on track to face the largest number of migrants along the southern border in two decades, after arrivals plunged in 2020 due to the COVID-19 pandemic. President Biden has continued pandemic-related ejections of most migrants, but unaccompanied children and some families have been allowed to remain in the United States. Over the past decade, the immigration system has come under increasing strain as thousands of unaccompanied children are now in U.S. custody, many of whom are held for days in border facilities that are not equipped for them. In 2021, apprehensions along the southern U.S. border reached an all-time high of 1.9 million, with the majority of arrests resulting in expulsion.

Where are most border crossings?

The southern 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. In recent years, the greatest number of apprehensions have occurred along the easternmost part of the border, called the Rio Grande Valley sector, in Texas. However, the Trump administration built fewer new border barriers in that sector than in any other, partly because it struggled to procure land from private owners. 

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 has risen in recent years. Over the past decade, many have been asylum-seeking minors and families from the Northern Triangle countries of El Salvador, Guatemala, and Honduras. They have fled gang recruitment, protection rackets, abusive police, inept criminal justice systems, and poverty. In 2021, the COVID-19 pandemic and persistent instability pushed more Central Americans to migrate north; that same year also saw an increase in migrants from Brazil, Ecuador, Haiti, and Nicaragua.

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Who is responsible for U.S. border security?

Securing the borders primarily falls to U.S. Customs and Border Protection (CBP), a branch of the Department of Homeland Security. Alongside agencies such as the Transportation Security Administration and Drug Enforcement Administration (DEA), CBP is responsible for overseeing 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 ports of entry, patrols thousands of miles of border to the country’s north and south, and helps investigate criminal networks, among other work [PDF]. Of CBP’s more than sixty thousand employees, nearly 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 in recent years to assist border agents with unauthorized immigration and drug trafficking. 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. National Guard soldiers can be called to action by either a state governor or, in some cases, the president.

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In 2018, National Guard personnel 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 to provide aerial and mechanical support. By August 2020, the Pentagon had sent up to about 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. At the same time, several Republican governors, including those from Arizona, Arkansas, and Florida, deployed thousands of National Guard troops to the Texas-Mexico border, many of whom are still there. 

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 nearly six 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 President Donald Trump made immigration a core issue. 

Since then, the number of active-duty troops assigned to the southern border has varied. It notably rose in early 2019 after the Pentagon deployed thousands more troops. In April 2020, the Pentagon sent roughly 540 additional active-duty personnel to provide surveillance and prevent migrants from entering the United States as the country battled COVID-19. Nearly four thousand troops, a mix of active-duty and National Guard personnel, are currently stationed at the border. Most are scheduled to remain there until September 2022.

What are the rules of engagement?

The 1878 Posse Comitatus Act limits the U.S. military’s role in enforcing domestic laws, meaning that interactions between active-duty troops and migrants at the Mexican border are restricted. They can neither detain and deport unauthorized immigrants nor conduct searches and seizures. Like the National Guard soldiers, they largely provide indirect support, such as conducting aerial surveillance and repairing or reinforcing infrastructure. Unlike the National Guard and CBP, 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 to affect an arrest,” 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.

Border Patrol
Border Patrol agents apprehend migrants at the southwestern border. John Moore/Getty

CBP personnel face hundreds of assaults each year. In fiscal year 2021, more than six hundred officers and agents were attacked while on duty at the southern border. The annual number of incidents involving use of force by CBP personnel has risen steadily since at least 2017, and more than two hundred 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. DHS Secretary Kirstjen Nielsen said in 2019 that CBP had blocked more than three thousand people with terrorist-like travel patterns or connections to terrorism from entering the United States at the southern border. The Washington Post challenged these figures, and some state governors recalled their National Guard personnel due to skepticism that the situation there constituted a national security crisis.

In 2019, Trump declared a national emergency—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. The move triggered dozens of legal challenges, but the Supreme Court allowed the administration to begin using diverted funds pending litigation. 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. As for drugs, CBP data shows that more are seized at legal ports of entry than between them.

How did Trump change the asylum process?

As a signatory to the 1967 protocol to the UN refugee convention, 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 in the United States as well as those arriving at 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.

Zero tolerance. With long waits at ports of entry driving more and more asylum seekers to cross at unauthorized points, the Trump administration implemented a blanket “zero-tolerance” policy by which it sought to criminally prosecute all adults who crossed the border illegally, including asylum seekers. (Such prosecutions were relatively infrequent [PDF] under Presidents Bush and Obama.) Under the policy, the government separated children from their parents and detained minors; though Trump signed an executive order in 2018 to end separations, they continued. In fiscal year 2019, his administration prosecuted a record number of people for immigration-related offenses, including more than twenty-five thousand for felony illegal reentry and nearly eighty-one thousand for misdemeanor improper entry. 

Narrower criteria. In 2018, Attorney General Jeff Sessions narrowed the criteria for asylum [PDF], instructing judges that gang or domestic violence generally does not qualify as grounds for asylum. Trump signed an executive order later that year denying migrants the right to seek asylum outside ports of entry. However, federal courts blocked both of these moves.

Migrant Protection Protocols. In 2019, a new policy called the Migrant Protection Protocols (MPP), also known as the “Remain in Mexico” program, began requiring asylum seekers from most Latin American countries 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 apply for asylum in Mexico, but they frequently face unsafe conditions, and the country’s bureaucracy is already stretched beyond its capacity to process claims.

Pandemic restrictions. Claiming asylum became even more difficult during the COVID-19 pandemic after the Trump administration implemented Title 42, an emergency public health order that allows border authorities to swiftly expel migrants, including asylum seekers.

Success rates for asylum seekers vary widely by court, but are overall quite low, often less than 10 percent. A growing backlog in the immigration courts—nearly 1.6 million cases as of December 2021—has meant long waits for claims to be heard; still, most asylum seekers appear for their hearings. Many who lose their cases become undocumented.

How is Biden responding?

Biden has dismantled several Trump-era policies while preserving others. He quickly suspended construction of the southern border wall and rescinded Trump’s national emergency declaration. His administration also officially ended the zero-tolerance policy and has sought to end the controversial MPP, but the Supreme Court has ordered the program to proceed while legal challenges continue. The administration continues to expel most migrants under Title 42 and Title 8, an order that allows Border Patrol agents to send back undocumented migrants. However, the administration is reportedly planning to lift Title 42 in May 2022, though some officials have said doing so could result in a surge of more than 170,000 migrants across the border.

Meanwhile, it has reopened temporary facilities to house the swelling number of unaccompanied child migrants, who are allowed to stay in the United States; dispatched officials from the Federal Emergency Management Agency to help process them; and ramped up their releases to sponsors.

Biden has pledged to comprehensively reform the U.S. immigration system. He sent Congress an immigration bill that would expand border surveillance, increase oversight of border authorities, and create new standards for CBP’s treatment of migrants. A subset of this bill known as the American Dream and Promise Act of 2021 was approved by the House of Representatives but has not passed the Senate. Biden’s plans also focus on helping Central American countries address the root causes of migration: the proposed legislation would provide $4 billion in new aid for this regional strategy. In March 2021, Biden named Vice President Kamala Harris to lead the U.S. response.

Recommended Resources

CFR’s Paul J. Angelo analyzes why so many Central Americans are arriving at the U.S. southern border and how the Biden administration is responding.

The Congressional Research Service explains CBP’s powers and limitations [PDF].

After traveling the U.S. southern border, USA Today offers a deep dive into life along the boundary and the implications of the wall.    

This CFR Backgrounder looks at the detention of child migrants in the United States.

This CFR Info Guide lays out the shrinking options for refugees.

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Michael Bricknell and Will Merrow created the graphics for this Backgrounder. Antonio Barreras Lozano, Zachary Laub, and Avery Reyna contributed to this report.

For media inquiries on this topic, please reach out to [email protected].

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