President Donald Trump vows to remove millions of unauthorized migrants from the U.S. and stop new entrants at the border. Bringing back the punitive playbook from his first administration not only won’t fix today’s border challenges. It will further destabilize Mexico and exacerbate threats to both countries.

Congressional Republicans have taken the anti-immigrant cue, holding an early hearing bent on reviving restrictive border policies. The migrant Protection Protocols, colloquially known as “Remain in Mexico,” forced asylum seekers to await their case hearing in Mexico.

Title 42 was even more ambitious in its exclusion, using the COVID-19 pandemic health emergency to expel migrants apprehended at the border. And yes, building the wall is back in vogue, albeit without talk of getting Mexico to pay for it.

These policies missed the mark in terms of slowing or stopping unauthorized migration and hurt Mexico and the U.S. Under Remain in Mexico, tens of thousands of asylum seekers duly waited next door as their applications were processed, living in makeshift camps and shelters for weeks, months, even years along the border.

The influx overwhelmed border towns and communities and attracted transnational criminal organizations, whose thugs assaulted, kidnapped and extorted migrants, forcing some to smuggle drugs into the U.S.

And while Title 42 blocked more than 2.5 million border crossings between 2020 and 2023, it didn’t stop migrants from coming. Indeed, during its first year in operation, border apprehensions between ports of entry nearly tripled, because the rapid, no-trace expulsion process encouraged migrants to keep trying to cross. There is no reason these policies will work better the second time around.

Adding now to the injury will be mass deportations. Roughly four out of every ten unauthorized migrants in the U.S. are from Mexico, potential targets for an aggressive round-up. Moreover, in perhaps a global first, Mexico has agreed to take in up to 30,000 deportees a month from other nations, a compromise the new administration could lean into and expand.

The influx of migrants passing through and being sent back across the border has been a boon to Mexico’s cartels, which have banked billions from their smuggling and extortion rackets. With estimated earnings from preying on migrants ranging from $4 billion to $12 billion a year, revenues now may rival those from illegal drugs.

Mass deportations will expand these opportunities. More desperate dislocated people mean more profits, which the gangs will use to expand their control of Mexico’s territory and its politics. Greater resources also give them more capacity to arm themselves and bribe officials on both sides of the border, boosting their deadly trades in fentanyl and other drugs.

Rising insecurity in Mexico hits legal commerce as well. A growing number of U.S.-based factories and producers depend on Mexico through an ecosystem of cross-border suppliers developed over the last three decades. Trade between the U.S. and Mexico has grown by more than 50% since 2020 and now tops $900 billion a year.

Nearshoring is a big part of the story. Mexico-based industrial parks have proliferated as manufacturers look to delink, at least in part, from China. The boomlet in Mexico-based assembly and manufacturing also drives demand for U.S.-made capital goods, machinery, and all kinds of parts and inputs.

A destabilized border threatens these gains. The U.S. got a taste of the cost in 2023, when migrant worries led the U.S. border patrol to stop trains coming into Eagle Pass and El Paso, Texas.

Auto makers, farmers, and ranchers in particular saw parts and agricultural products pile up on both sides of the border. Mass deportations could expand and extend the chaos, threatening many of the more than one million U.S.-based jobs that depend on exports to Mexico, and the many more tied into North American supply chains. The effects would reach far beyond the border, as Mexico is a top export destination for over half of the U.S. states.

Border turmoil will make it harder for President Claudia Sheinbaum to sustain, let alone expand, Mexico’s cooperation with the U.S. to reduce migrant flows.

In addition to agreeing to implement Remain in Mexico during Trump’s first term, the nation has beefed up controls at its southern border and broken up caravans of migrants moving north. It has stopped trains the sojourners ride and intercepted and bused migrants from northern to southern Mexico, away from the U.S. border. It has worked with the U.S. to target migrant smuggling networks.

But policies such as the decision to accept tens of thousands of non-Mexican deportees aren’t popular in Mexico. According to polls from Latinobarometro, Oxfam Mexico, and Parametria/El Pais, roughly half of Mexicans think migrants take jobs and increase crime and are harmful to the nation more generally. A third want Mexico to limit migration, a fifth want the government to block migrants entirely.

Mexico looks near its breaking point in absorbing migrant flows. Its National Institute of Migration is underfunded and overwhelmed. Its asylum system is paralyzed by a backlog of 300,000 applications, even as 100,000 new claims are filed each year. An exodus of U.S. deportees would likely harden these underlying public animosities, making it harder for Sheinbaum to go along with U.S. policies.

To protect its commercial ties and its communities, the U.S. needs orderly migration at the border. Late in Biden’s term, this started to happen. Tighter asylum rules and broader use of the CBP One app to schedule appointments substantially reduced the number of people showing up at border crossings each day and those crossing between legal ports of entry. So did the opening of new legal humanitarian pathways. Over the last year, encounters at the border have fallen some 80%.

Reintroducing stringent border laws, shutting down the CBP One app that regulates appointments, ending newer legal avenues into the U.S., and many other restrictive changes won’t make the border more orderly or likely even reduce unauthorized migration. Deporting those already here to Mexico certainly won’t either. Instead, it will aggravate security challenges and weaken economic ties that benefit both countries.

Last February, Trump torpedoed a bipartisan bill that would have strengthened border enforcement, targeted the cartels, raised the legal bar for asylum and hired more immigration judges and asylum officers. That U.S. law would have helped. One other reality is inescapable, however: The real solution to fixing the border must be not only bipartisan, but bilateral.

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This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

Shannon O'Neil is a senior fellow for Latin America studies at the Council on Foreign Relations and author of "The Globalization Myth: Why Regions Matter."

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