Explaining and Predicting: The Evolving Dynamics on the U.S. Southern Border

As the immigration debate heats up in the public discourse and Congress, this Explainer assesses how immigration dynamics in the U.S. have evolved under Presidents Biden, Trump, and prior administrations, and—more importantly—what to expect in 2024 and beyond.


Source: AP/Gregory Bull.

On Wednesday, House Republicans voted to advance impeachment articles against Department of Homeland Security (DHS) Secretary Alejandro Mayorkas, moving closer to make Mayorkas the first Cabinet secretary to be impeached in nearly 150 years. The articles allege he violated immigration laws that require the detention of all migrants—something no administration has ever done—as well as breaching “public trust.” However, notable conservative legal experts have signaled those arguments fall well short of the high crimes and misdemeanors standard set out in the constitution. Meanwhile, the Senate is also considering a bipartisan bill to improve border security, though it faces considerable opposition from former President Trump, House Speaker Mike Johnson, and other Republican legislators—even though Democrats are embracing the toughest posture on immigration in decades. As the immigration debate heats up in the public discourse and Congress, this Explainer assesses how immigration dynamics in the U.S. have evolved under Presidents Biden, Trump, and prior administrations, and—more importantly—what to expect in 2024 and beyond.    

Q1: How have U.S. border dynamics evolved in recent years? How can congressional action change the situation on the southern border?   

Immigration to the U.S. looks significantly different today than it did 20 years ago. Both the scale and origin of migrants heading northward have shifted noticeably. In 2000 the U.S. apprehended close to 1.7 million migrants–a record at the time–with the majority of migrants coming from Mexico and Central America. In the years since, the predominance of Mexican and Central American migrants has been replaced by arrivals from elsewhere in the Western Hemisphere and beyond. Today, Mexicans and Central Americans no longer make up a majority of apprehensions, while 2023’s 2.5 million apprehensions broke yet another record.   

What often gets lost in the discussions on immigration is that until fairly recently, most people crossing the border were able to do so without being apprehended. In 2000, the U.S. only had some 10,000 border patrol agents, meaning an estimated 60 percent of migrants were able to cross without apprehension. Since the establishment of the Department of Homeland Security (DHS) after 9/11, successive administrations have scaled up Customs and Border Patrol (CBP) and its capacity to apprehend migrants. Today, CBP has close to 20,000 agents and now less than 20 percent of migrants are able to cross the border unapprehended. Ironically, the authorities’ improved presence and effectiveness at the border contributes to the sense of a worsening border crisis. However, the numbers show the opposite. Whereas before migrants got through with ease and went unnoticed, today more apprehensions make it clear that migrants are trying to cross but are failing to do so.

Congressional action would ramp up CBP’s capacity. At the moment, Senate leaders from both parties are supporting a bipartisan compromise which links Ukraine and immigration funding. The current proposal would pay for 1,300 more border patrol agents, more asylum officers, and hundreds of judges. Even still, the path toward passing a bill to increase CBP funding remains unclear as the more conservative elements of the Republican party have suggested that a compromise would become a political liability for the upcoming elections. Thus Border Patrol’s capacity to weather subsequent surges in migration depend on if and when leaders on Capitol Hill can agree to put aside their political differences on the other half of the bill–namely, funding for Ukraine.         

Q2: What is the Biden administration’s record on immigration and what do current trends suggest for the U.S. in 2024?

Despite criticism from both his right and left, President Biden has navigated surging arrivals at the border and a global pandemic with unprecedented executive action. Over the past three years, his administration has taken over 500 executive immigration actions, becoming the most forward-leaning president on the issue in U.S. history. Under the controversial Title 42, which ended in May 2023, both Biden and former President Trump rapidly expelled migrants due to the extraordinary circumstances of the pandemic. However, President Biden has removed a higher percentage of border crossers under Title 42 than Trump did (51 percent versus 47 percent), despite Trump having had to deal with many fewer total crossings.

Since Title 42 ended, the administration has pivoted to a program which incentivizes arrivals at ports of entry and disincentivizes irregular crossings. Under the administration’s new system, migrants must apply for asylum through a CBP application, known as CBP One. Without an appointment through the application, migrants cannot receive asylum unless they had applied for and been denied protection in another country, arrived through a parole program, or qualified for an exception under the rule. The new system has led to mixed results. Although more migrants are using safe and orderly channels of entry through official ports, irregular arrivals have also remained high, leading the President to ask Congress for an additional $14 billion to augment U.S. border security.

Going forward, cementing migration policy hinges on election results, and 2024 has the potential to shape migration policy for the foreseeable future. Donald Trump has vowed to curb illegal immigration by building more miles of the border wall, reinstating the “Remain in Mexico” policy, and deputizing the National Guard to carry out mass deportations. In Venezuela, Dominican Republic, and Panama elections will also play a pivotal role in shaping regional cooperation. Overall, high numbers of economic- and security-driven refugees look to pose a considerable policy challenge for candidates in the U.S. and the region.   

Q3: What role will immigration play in determining who will win the U.S.’ 2024 election? 

Immigration is likely to play a major role in the 2024 U.S. election, particularly if Joe Biden and Donald Trump are the candidates. According to Gallup, immigration is the top non-economic concern among U.S. voters. Similarly, earlier polling from Pew Research suggests that registered Republicans view immigration as a top issue while registered Democrats are significantly less concerned.  

External events such as the high-profile border incidents Americans witnessed in 2014, 2019, and 2021 could shift the narrative and influence voter perceptions further. Since any new development would happen during the Biden administration, this would more likely hurt Biden and benefit Trump. However, Biden’s record on immigration is more forward leaning. And, if Congress is able to pass immigration funding measures in the coming weeks and months, then Biden’s credibility could be bolstered, as he may be seen as a leader who can get both sides of the aisle to compromise. Further complicating matters, former President Trump has called upon allies in the House and Senate to oppose the bill to deny President Biden a legislative victory, calling it a “gift to the Radical Left Democrats” who “need it politically.” If the bill fails, it will be viewed as a loss for Biden and vindication for Trump who believes he benefits from inaction.     

Therefore, while immigration is likely to be a significant issue in the 2024 election, its exact role in determining the outcome will depend on evolving external events, and how the candidates’ respective responses to such events as well as their past records.  

Q4: What role does Mexico play in the U.S. immigration strategy?

Though Mexicans no longer represent a majority of arrivals in the U.S., today, the U.S.-Mexico border remains the world’s largest migration corridor. Every year Mexico receives hundreds of thousands of migrants from different parts of the world, including Central America countries, Haiti, Ecuador, Colombia, Venezuela, and China, looking to cross to the United States. Containing the influx of migrants poses a significant challenge for the Mexican authorities. So far, in light of the recent shifts in migration policy under Republican and Democratic administrations, the Mexican government has opted to mostly accommodate the U.S., carrying much of the burden and responsibility of interdicting migrants and hosting asylum seekers.

Under former President Trump, migration became a contentious issue in the bilateral relationship. In 2019, Mexican President Andrés Manuel López Obrador’s initial “open door” human rights-based approach on migration changed after the Trump administration threatened to impose tariffs if his administration did not halt illegal migration. Adopting a pragmatic approach, López Obrador reversed course and implemented a hard line migration policy, increasing migrant apprehensions, restricting humanitarian visas, and deploying Mexico’s National Guard for migration enforcement. 

Today, López Obrador understands the importance of migration to U.S.-Mexico relations. Indeed, Biden’s administration’s less restrictive migration policy, geared toward addressing the “root causes of migration,” offered the opportunity for López Obrador to gain leverage. Democrats’ concerns over democratic erosion in the region and AMLO’s authoritarian tendencies and controversial energy reform, have complicated coordination on major policies including migration. Unlike his experience with the Trump administration, today it is López Obrador, willing as he is to crack down on migration, who has the leverage on the U.S.-Mexico relations. 

That said, Claudia Sheinbaum, former Mexico City mayor, and the leading candidate in Mexican polls, could change Mexico’s position on migration, adopting a more combative and human rights centered approach. At a campaign event on the border she declared that Mexico should never accept anything less than equal footing in the U.S.-Mexico relationship. At a separate event in Los Angeles, she also asserted that she would fight for Mexicans in the United States for immigration reform. With these statements in mind, it is therefore very likely that migration will continue to be a contentious issue for the U.S.-Mexico relationship regardless of who assumes the presidency in the U.S. 

Q5: The stated policy of the Biden administration has been to tackle the “root causes” of migration in Central America at the source. What results has this strategy yielded in addressing irregular migration from the region? 

In President Biden’s first year in office, political opposition to the ‘root causes’ approach to migration derailed the U.S. Citizenship Act, which would have dedicated $4 billion dollars of development assistance to the Northern Triangle (Guatemala, Honduras, El Salvador). Nevertheless, Northern Triangle countries received over $4 billion in investment thanks to Vice President Kamala Harris’ public-private partnership initiative and $1.87 billion in U.S. development assistance. 

Given the many contributing factors influencing migration, it is difficult to judge the success of Biden’s policy. The ‘root causes’ approach was never meant to be a quick fix, and experts maintain that the initiative will only be successful with long-term, consistent political support. Nevertheless, corruption, violence, and inequality remain serious drivers of migration in the Northern Triangle. U.S. Border Patrol reported far fewer encounters with nationals from Northern Triangle countries in 2022 and 2023, but the COVID-19 pandemic and hurricanes Iota and Eta may have disproportionately increased migrant encounters in previous years. As migration from the Northern Triangle has eased, new crises have created new migration sources, including Cuba, Haiti, and Venezuela mainly, demonstrating that the ‘roots’ of migration are not limited to the Northern Triangle.

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