One of the big changes we should expect under a Joe Biden administration is an explosion of illegal immigration and a renewed crisis at the U.S.-Mexico border. The reason for this is simple: the immigration and border policies the Trump administration has put into place over the past four years have succeeded in driving down illegal immigration, and Biden has promised to reverse nearly all of them.

Throughout the campaign, Biden was forthright about his plans to dismantle Trump’s immigration and border security agenda. His team is now planning to carry out those plans, including a 100-day moratorium on deportations, directives to curtail arrests of illegal immigrants, and a full restoration of the Obama-era Deferred Action for Childhood Arrivals program, or DACA.

These actions will almost certainly trigger a wave of illegal immigration up and down the southwest border. Why? Because Trump’s policies helped bring illegal immigration under control. Undoing them will be interpreted, rightly, as an invitation to would-be migrants in Mexico and Central America, who will respond accordingly, especially as those countries continue to suffer from worsening conditions under the pandemic.

Although pandemic restrictions and border security policies in the United States and Mexico helped decrease the number of apprehensions at the southwest border over the summer and fall, illegal immigration was steadily declining long before the outbreak, largely because of programs and policies implemented by the Trump administration in response to a dramatic rise in illegal border crossings and apprehensions in 2019.

The Migrant Protection Protocols, or the “remain in Mexico” program, which requires most asylum-seekers to wait in Mexico for their cases to be heard by a U.S. immigration judge, has been one of the most prominent—and controversial—Trump administration policies aimed at curbing illegal immigration. In cooperation with the Mexican government, it has also been successful at deterring illegal immigration and reducing specious asylum claims.

Since the program’s inception in late 2018, some 67,000 people have been returned to Mexico after having been caught crossing the border illegally. Many of these migrants have opted to return to their countries of origin, citing dangerous conditions in Mexico and the likelihood they will lose their asylum cases in court. Biden has said he will end the program.

Another major action taken by the Trump administration was the termination of the Flores Decree, a 1997 court decision that prevented U.S. officials from detaining migrant families and unaccompanied minors for more than 20 days. Because Flores all but guaranteed that an adult who crossed the border with a child would, upon claiming asylum, be quickly released into the United States, it created a powerful incentive for families to cross the border illegally and make questionable asylum claims.

It also fueled a lucrative and exploitative human smuggling industry stretching from Central America to the Rio Grande. Flores meant children were used as “passports” into the United States—not just by families but also by unscrupulous smugglers and cartels that profit handsomely from illegal immigration. U.S. officials discovered thousands of “fake families” at the border in recent years, with adults posing as parents of unrelated children, and even cases where children were “recycled,” crossing the border multiple times with unrelated adults.

By ending Flores, the Trump administration was able to more or less end this practice, since it removed the promise of a quick release if you had a child with you and claimed asylum. Biden has said he will effectively reinstate Flores, releasing asylum-seekers who arrive with children before their court dates and funding various case-management programs in hopes that they don’t simply disappear into the immigration underground once they are released.

Biden has also said he will restore DACA, the Obama-era program that allowed illegal immigrants who were brought to the U.S. as minors a reprieve from deportation and renewable, two-year work permits. The promise of minors being allowed to stay in the United States helped fuel a surge of unaccompanied children and teenagers to the border beginning in 2014, with smugglers promising parents that they and their children would be granted “permits” to remain in the United States.

It didn’t matter that DACA didn’t actually apply to these minors. Unscrupulous smugglers, known as “coyotes,” sold families on the line to pocket their passage fees, with cartels taking their cut at the Rio Grande.

The Trump administration announced it was ending DACA in 2017, but the U.S. Supreme Court ruled in June that the administration hadn’t followed the proper procedures for ending the program, leaving it for the time being in administrative limbo. Even so, as the case has been wending its way through the courts the past few years, the message has gotten back to sending communities in Mexico and Central America that unaccompanied minors don’t have a guaranteed way to stay in the United States through DACA. Once Biden restores it, they will.

Another Border Crisis Is Already Brewing

All of these changes promised by the Biden administration will not go unnoticed by would-be migrants seeking entrance to the United States, or by the smugglers and cartels who profit off getting them here. Messaging and sometimes even minor U.S. policy changes have a ripple effect on the migration pipeline that runs from South Texas all the way to Guatemala City and Tegucigalpa.

What’s more, Biden need not have the cooperation of Congress to do these things. Indeed, Trump didn’t have congressional support for most of his immigration and border policies, and neither did President Obama. Most Americans don’t realize it, but U.S. immigration law gives wide latitude to executive branch agencies like the Department of Homeland Security and U.S. Customs and Border Protection to create and implement policies at the border, from the detention and processing of migrants caught crossing illegally to the procedures and requirements for asylum adjudication.

That’s partly by design: Congress has long abdicated its responsibility for immigration, instead delegating authority and policy-making to an ever-growing executive bureaucracy.

That means every time the White House changes hands, U.S. immigration and border policy goes through a massive upheaval. All along, Biden has been candid about his plans for the border, and if he follows through on them—like Trump, mostly via executive order—it will trigger a wave of migration from Central America and Mexico that U.S. border officials will be largely powerless to stop.

To suppose otherwise is not only to ignore recent history, but to assume that the people of Mexico, Honduras, Guatemala, and El Salvador have no agency. Already in late September, at least one large caravan was reportedly forming in Honduras, headed for Mexico and the U.S. border.

Others will follow under a Biden administration, their ranks filled with people drawn by the resurrection of Obama-era policies that will grant them, by various mechanisms, entry to the United States. They will be making a rational and reasonably informed choice. And on understanding just how drastically U.S. immigration policy can shift with a presidential election, and how much easier it will be to get in under Biden, they won’t be wrong.