A historic uptick in migration during Joe Biden’s presidency led to attacks as he ran for reelection, with Donald Trump and fellow Republicans blaming Democrats for the swelling number of people crossing the U.S.-Mexico border.
Now, after campaigning on promises to secure the border and deport undocumented immigrants, President-elect Trump is poised to take office Monday amid a steep drop in border crossings.
Here are five key facts about migration across the U.S.-Mexico border over the last several years.
1. Arrivals at the border are the lowest they’ve been since Trump left office
When Trump left office in January 2021, people were stopped at the southern border more than 78,000 times that month, according to figures from the U.S. Customs and Border Protection. That’s compared with roughly 96,000 stops last month. The highest monthly total during the Biden administration was nearly 302,000 in December 2023, and Trump’s highest total was just over 144,000 in May 2019.
These figures include arrivals at land ports of entry, where asylum seekers wait for appointments to enter legally, as well as those caught crossing illegally elsewhere along the border. Figures from November and December showed, for the first time, more migrants being processed through ports of entry than those who were arrested after entering the U.S. illegally.
In June, the Biden administration began effectively blocking migrants from seeking asylum along the U.S. border with Mexico. The restrictions don’t apply to those who enter at official ports of entry or use other legal means.
For parts of last year, San Diego became the top destination for illegal crossings along the U.S.-Mexico border for the first time in decades. The change reflects how smuggling routes, which used to be consistent for many years, have begun to shift every few months since 2021. That’s in part because of the post-pandemic increase in global migration to the U.S.
The San Diego region saw 10,117 border arrests in December — the second-highest after the Rio Grande Valley in Texas — though that’s down by 70% from a year earlier.
2. There hasn’t been much of an increase in border arrivals ahead of Trump’s inauguration
In the weeks leading up to Trump’s inauguration, most regions across the border have seen little change in arrivals of migrants. But Chief Border Patrol Agent Gloria Chavez of the Rio Grande Valley Sector in south Texas, who posts local arrest numbers on social media every week, reported 1,206 migrant stops over the final weekend of December, and 1,276 the weekend before. That’s double the number in recent weeks of fewer than 600 arrests.
“It is the first quantitative indicator of an increase in migration since the U.S. election, which raised expectations — so far unmet — that many migrants might rush to enter the United States before Election Day,” Adam Isacson, director of defense oversight at the advocacy organization the Washington Office on Latin America, wrote in a recent newsletter.
That trend appeared to have waned in the new year, with Chavez reporting 669 arrests the weekend that ended Jan. 5 and 699 arrests the weekend that ended Jan. 12.
Isacson noted that in 2016, asylum seekers rushed to enter the U.S. before Trump began his first term. But border policies are different now, with Biden administration rules already preventing most people who enter illegally from qualifying for asylum.
“Their only hope is to not be apprehended,” he said. “Some people might be trying, and if they’re successful they won’t show up in the numbers.”
Aaron Reichlin-Melnick, a senior fellow with the left-leaning American Immigration Council, said tens of thousands of migrants are waiting in Mexico.
“Today it is harder for migrants to make it to the border and seek asylum than at any point in modern U.S. history,” he said. “Despite this massively increased infrastructure at the border, the U.S. continues to remain, in the eyes of people around the world, a place of safety and security.”
3. The U.S. border used to draw mostly Mexican and Central American migrants. Now people from all over the world flock here
The U.S. has historically drawn migrants from its southern neighbor. Although Mexicans still make up the highest proportion of those seeking entry, arrivals of people from other countries have shot up over time. During Trump’s first term, people from Honduras, Guatemala and El Salvador flocked to the U.S. border due to instability in their home countries.
That started to change around 2019. Throughout Biden’s presidency, greater numbers of people began to arrive from Venezuela, Cuba and Colombia. People also came from farther away — Afghanistan, Ukraine and China.
The San Diego region has what is considered the most international border, drawing people from all over the world.
Chinese migrants in search of jobs and freedom from the repressive government there started arriving in record numbers — increasing from just 949 arrests in fiscal year 2022 to more than 37,000 last fiscal year. Republicans seized on the increase, painting it as a national security issue.
Numbers began to decrease last year after the Biden administration imposed asylum restrictions and Ecuador began requiring Chinese nationals to have a visa to fly there.
4. Immigrant detention has ramped back up since COVID-19 decreases
The government’s operation for detaining people who violate immigration laws has seen wild swings in recent years. During Trump’s first term, the population detained by Immigration and Customs Enforcement reached historic highs of more than 55,000 people.
As COVID-19 spread through lockups, killing detainees, courts ordered some immigrant detention centers to reduce their populations. The detention population reached a low of about 13,000 people in February 2021, the month after Biden took office. (The Adelanto ICE Detention Facility east of Los Angeles has remained under a COVID-era court order that prevented new detainees, dwindling the population of the nearly 2,000-bed facility to just two people.)
As of Dec. 29, more than 39,000 people (most of whom have no criminal record) are being held in civil immigrant detention facilities, according to TRAC, a nonpartisan data research organization. That number has remained fairly steady for the last year, generally fluctuating between 35,000 and just under 40,000 since late 2023.
Numbers are widely expected to increase again after Trump takes office, as he works to make good on his promise of mass deportations.
5. Historic arrivals under the Biden administration added to the already enormous backlog in immigration court
Immigrants placed in deportation proceedings can plead their case before an immigration judge. With historic arrivals of migrants under the Biden administration, the immigration court backlog now has more than 3.7 million pending cases, according to TRAC.
Biden inherited an already backlogged immigration court system with 1.3 million cases. When Trump assumed office in 2017, just over 542,000 cases were pending.
In fiscal year 2024, immigration courts closed more than 900,000 cases — the most of any single year. New cases have fallen sharply as fewer immigrants are processed at the border.
Los Angeles County has nearly 115,000 cases, the second-highest after Miami-Dade County. Experts say the backlog can’t be eliminated without funding hundreds more immigration judges and support staff, as well as systemic reforms.