The U.S.-Mexico border is once again dominating a U.S. presidential election.

With voters ranking immigration high on their list of concerns, both Democratic presidential candidate Kamala Harris and Republican contender Donald Trump have been pledging to boost border security and curb the flow of asylum-seekers across the country’s southern border.

As an academic researcher and the daughter of immigrants, I wanted to understand what restrictive migration policies have accomplished in the past. Digging into newspaper archives, government reports and accounts by nongovernmental organizations from the early 1990s to the present, I found that while laws and policies intended to slow migration at the U.S.-Mexico border have not generally curbed migration, they have consistently led to more migrants dying along the journey.

I also found that mobile phone-based innovations meant to make asylum safer and easier may not help as much as intended.

More migration

Since 1993, decades of economic instability, political instability, intensifying violence and the effects of climate change across Latin America have spurred increasing migration rates into the U.S. as people flee life-threatening situations. In 2023, U.S. Customs and Border Protection reported approximately 2.5 million apprehensions and deportations of migrants at the U.S.-Mexico border. That’s up 750% since 1992.

This uptick in the early 1990s roughly coincided with Operation Blockade, a federal government effort to tighten security at the then-relatively porous border checkpoint in El Paso, Texas. By stationing about 450 border patrol officers across a 20-mile stretch of border to verify that all people entering the U.S. had a visa or other authorization, the U.S. aimed to stop unlawful crossings in El Paso.

To avoid documentation checks, a growing stream of migrants began taking longer and more dangerous routes through the desert to cross into the U.S.

Many of them were asylum-seekers, fleeing persecution and other dangers at home, whose goal was to reach the U.S. and file a claim for asylum protection. This is called filing a “defensive” asylum claim, as opposed to an “affirmative” claim, which is filed before traveling to the U.S.

It’s a once-common process that’s gotten only more difficult in recent years. During the COVID-19 pandemic, the Trump administration’s Title 42 began requiring migrants to stay in Mexico and file their affirmative U.S. asylum claim from there. After that rule lapsed in May 2023, the Biden administration created a new federal rule allowing border officials to deny asylum to almost any migrant at an official port of entry along the U.S.-Mexico border who has not previously applied for asylum en route to the U.S.

This new rule requires asylum-seekers to request affirmative asylum – that is, before they arrive at the border – using U.S. Customs and Border Protection’s new mobile phone app, CBP One.

This mobile phone innovation was meant to streamline the asylum process. The app is notoriously glitchy, however, and the agency did not add enough additional time slots to its calendar for the flood of new affirmative asylum appointments that would otherwise have been “defensive.”

Unable to cross legally into the U.S. until their claims are filed, asylum-seekers now remain trapped on the Mexican side of the border for an average of seven months awaiting their appointment with Customs and Border Protection.

Migrants staying at shelters in Mexican border towns say they live in fear that the persecutors they fled will find them there. They are also vulnerable to the violence and kidnapping targeting asylum-seekers along the border.

Death now or later?

As the U.S. has hardened security at official border checkpoints over the years, as it did in El Paso, migrants have in turn taken to crossing the border in the remote reaches of Arizona’s Sonoran Desert.

This treacherous route has made an already dangerous trek even more deadly. The U.S. Government Accountability Office found that border-crossing death rates had more than doubled from 1995 to 2005 despite no increase in the number of recorded migrant entries into the U.S. during this time period.

In 2023, nearly half of the 686 migrants who died trying to cross the U.S.-Mexico border died in the Sonoran and Chihuahuan deserts, mainly from extreme heat and cold. Before Operation Blockade, less than a third as many people died trying to make their way into the U.S. – 205 in 1993.

“The punishment handed out by difficult terrain” is its own migration policy, to paraphrase scholar Jason De Léon in his 2015 book “The Land of Open Graves.”

In an effort to reduce migrant deaths in Arizona’s deserts, in 2008 the humanitarian organization Humane Borders negotiated with the U.S. Department of Homeland Security to have public safety communications equipment installed on the observation towers going up along the border that year. This equipment enabled migrants to call 911 – but nobody else – to request emergency services.

By calling 911, however, migrants expose themselves to deportation. A 2023 report by the humanitarian organization No More Deaths found that almost all 911 calls for help by suspected migrants in Pima County, Arizona, were redirected to Customs and Border Protection rather than receiving immediate search-and-rescue support. Border officials can then identify the caller’s location using the towers’ surveillance equipment, including radar, imaging sensors and edge computing hardware.

Like local emergency dispatchers, border officials are required to assess needs and provide emergency medical assistance. But they may also then detain unauthorized migrants for deportation.

“As soon as you try to call somebody to come for you,” one migrant told researchers in a 2017 study, border patrol agents “know where you are, and they will go looking for you.”

Those struggling with dehydration or injury face a grim choice. If they don’t call 911, they may die in the desert. If they do call, they may die later, either in U.S. immigration detention centers – where dozens of people die of preventable medical or mental health conditions each year – or back home, if they are sent back to the dangers they fled.

Research suggests that while some migrants do feel safer with a phone, knowing that they or their smugglers can call for help in case of emergency, others are too afraid of detection to carry or use their mobile device.

The opportunity to call for emergency aid has prevented some deaths in America’s borderlands. Tucson’s 911 call center reported receiving about 40 calls a day from the border region in 2021 alone. But restrictive border policies impede the mobile phone’s lifesaving potential.

The need and desire to migrate to the U.S. has only grown in recent decades, but the U.S.’s embrace of immigration has waned, with deadly consequences.

Angela Schöpke Gonzalez does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.