SAN ANTONIO — President Trump’s web of restrictive asylum policies lowered immigration levels, pushed many migrants away from U.S. borders and aimed to signal to people worldwide that it would not be easy to seek refuge in the country.

The U.S. government has historically allowed asylum seekers to enter the country to have their cases fully heard, part of a long-held ethos that the United States was a place where people could find safety from persecution. But as migrant flows shifted, including tens of thousands of unaccompanied children and Central American families, the Trump administration assumed that many claims were illegitimate and took steps to deter migrants by pushing most into Mexico to wait, narrowing the grounds for requesting asylum, limiting their legal options or outright expelling them from the United States.

Unraveling the programs, regulations and rules designed to shut out asylum seekers will not only be a major policy challenge for President-elect Joe Biden, but it probably will mean recalibrating a federal apparatus that has been used during the past four years to try to stop the majority of immigrants from coming.

Biden has vowed to bring a more humanitarian approach that ensures “the dignity of migrants” and upholds “their legal right to seek asylum,” according to his transition website. He plans to reverse Trump administration policies such as the Migrant Protection Protocols — a program that returned more than 65,000 asylum seekers to Mexico — and wants to send more asylum officers to the border to process cases.

When the coronavirus outbreak began in the United States, the Trump administration effectively closed the border to immigrants, leading many asylum seekers to abandon their claims, cross illegally or send their children across alone. The roughly 25,000 people still waiting under MPP are spread out across Mexico, and rescinding the program probably would mean allowing them into the United States for their hearings, one among many complex repercussions of undoing the policies of the past four years.

“If you pull one string, it can get messy pretty fast,” said Stephanie Leutert, director of the Mexico Security Initiative at the University of Texas at Austin. “It's policy after policy layered on top of each other. Each one is going to take a very long series of steps to unwind responsibly. If you want fair asylum access for everyone arriving at the border, you need to wipe away and restart.”

The possibility of returning to Obama-era policies that would allow asylum seekers possibly to disappear into the country before their cases are adjudicated disquiets federal immigration law enforcers. They predict that smuggling networks would go into hyperdrive, triggering a new illegal immigration rush.

“We can expect an influx,” said Brandon Judd, president of the National Border Patrol Council. “We can expect the pandemic to spread. I don’t think that’s speculative, I think that’s a flat-out fact.”

President Barack Obama presided over the early surge of mostly Central American families forced to flee to the American Southwest. Initially, he jailed refugees in detention facilities as a deterrent, and he deported millions.

Linda Rivas is an immigration attorney whose work regularly takes her to the dangerous Mexican border city of Juarez, where thousands of migrants are stranded. (The Washington Post)

During a similar surge of migration, Trump also tried to deter the masses with programs such as MPP, and his “zero tolerance” policy that included family separations.

Biden has said he is seeking a different path that will end “prolonged detention” and has vowed to discuss “region resettlement solutions” with foreign leaders. The former vice president has experience working with Central America after being Obama’s point person during the 2014 child migration crisis.

“The Trump administration worked to put a broader solution into place, but theirs was based totally on restriction and denying legitimate claims,” said Doris Meissner, a former commissioner of the U.S. Immigration and Naturalization Service and a senior fellow at the Migration Policy Institute. “What I’m expecting from a Biden administration is flipping those broader efforts on the border in ways that recognize there can be legitimate claims, but it needs to be done in a way that is orderly and leading to a change in the conditions that are driving the migration.”

Biden’s wife, Jill, visited the encampment in Matamoros, Mexico, where hundreds of migrants have lived while waiting for asylum, delivering tamales and Christmas gifts last year. She described the scene as heartbreaking and a living contrast to the symbolic promise of the American flag.

Nancy Avilés won’t forget that day. The Salvadoran migrant has held onto Jill Biden’s words like a psalm. The 40-year-old said she left her country in 2019 with her two children after gang members killed her husband. In the time they’ve waited for a hearing, Avilés’s son has had two birthdays and her daughter turned 18. Their March court date was canceled.

“Birthdays aren’t celebrations here,” Avilés said. “They are a reminder of how long we’ve waited for hope.”

The coronavirus pandemic plunged the encampment into darkness, leaving asylum seekers in limbo. Joel Fernandez Cabrera of Cuba was cautiously optimistic that Biden’s victory meant the president-elect would not forget them.

“Light has returned to the camp,” the 52-year-old said. “Biden has made a commitment to those of us trapped in MPP. We hope he fulfills his promises.”

In Nogales, Mexico, the Kino Border Initiative has assisted 499 migrants waiting under MPP this year. The group has led protests along Trump’s border wall and is planning a more direct plea to the Biden administration to end MPP.

Across northern Mexico, the mayors and governors of border states have spoken against the program since its inception. Those officials said their states didn't have the resources to support tens of thousands of migrants who would be waiting for months along the border, and suggested that they didn't have the resources to protect them. Mexico's federal government provided almost no support to those states to assist stranded asylum seekers.

Experts say Biden's success will hinge on Mexican cooperation and their own capacity to build asylum programs and protect migrants.

“It’s difficult for us along the border to receive so many people, especially in the middle of a pandemic, when we don’t have the resources to support them,” said Maki Ortiz, the mayor of Reynosa, across the border from McAllen, Tex. “These migrants also present an opportunity for organized crime who want to recruit them.”

Earlier this year, a report from Human Rights Watch found “at least 32 instances of kidnapping or attempted kidnapping of asylum seekers in the MPP program — mostly by criminal organizations — between November 2019 and January 2020.” Several asylum seekers have been found drowned in the Rio Grande.

Mexico’s government has said publicly that it did not agree to implement MPP, but that it had no choice but to accept them. But Tonatiuh Guillén López, a former Mexican immigration chief, has disputed that, saying the program was the product of a bilateral negotiation.

Guillén, who resigned after MPP’s implementation and is now a professor at the National Autonomous University of Mexico, said he was disappointed by what the program said about the Mexican administration’s agenda.

“Migrants — including Mexican migrants — haven’t been a priority of national politics, and now less than ever,” he said.

The Trump administration suspected that migrants were making disingenuous asylum requests because they knew their cases could take years to resolve. The U.S. government’s solution was to keep the vast majority of people outside U.S. borders and appoint more immigration judges to move cases along. Asylum denial rates climbed.

Biden has proposed adding many more asylum officers at the border to process cases efficiently, increasing the number of immigration judges to relieve backlogs and investing in case management to ensure that families allowed into the country attend all their court dates.

But Meissner said he could go one step further to restoring a meaningful asylum system by giving those officers the power to judge the full merits of a case.

“Immigration judges often are not as well-trained on country conditions as are asylum officers,” she said. “The cases that are approved don't have to go to immigration court and people can get on with their lives. The system then begins to correct itself and starts sending a signal about the kinds of cases that are meritorious and will be approved.”

Leutert, of the University of Texas, said the president-elect’s asylum plan leaves many questions unanswered.

“What do you do with the thousands of people who were denied or abandoned their claims? Who goes first?” she said. “Do you reopen cases for everyone or specific groups?”

Judd, of the National Border Patrol Council, said his members have their own questions about keeping agents safe and a possible return to policies they say incentivize smugglers and cartels to put people in danger.

“The administration did not listen to us,” Judd said of Obama’s presidency. “There’s a reason why we never endorsed anyone until Trump. It came to the point where we had no choice. He addressed the issues we brought to their attention. We had never seen it before.”

Sieff reported from Mexico.