TIJUANA — Martin Pina stands in the courtyard of the "Casa del Migrante," which was founded 29 years ago by Catholic Scalabrinian missionaries to help migrants in this teeming Mexican border city.

Sporting a tattoo of his mother Belinda on his left arm and Mexican singer Selena on his right, Pina says that he had been deported just four days earlier from California for selling marijuana. "I made mistakes, they found me and deported me four days ago," says Martin. " I've already done nine years of prison, and I would have had to serve another eight, and then a life sentence if they caught me again."

Pina is one of the three million "criminal" undocumented immigrants that President-elect Donald Trump has vowed to immediately deport from the United States. But Pina's wife and 22-year-old son, a natural-born U.S. citizen, are still on the other side of the border. "I think the new President will do what he promised, he would hang people like me if he could," he quips.

A small-time marijuana dealer, Pina is far from the drug kingpins Trump has vowed to bring to justice. "I'm just a small fry, I don't know the leaders of the Sinaloa Cartel that control this region," he says. "But this is the only way I can make a living, so what else can I do? If he builds the wall, we'll just climb over it or build tunnels under it, and if he deports us we'll just keep coming back."

A forbidding border wall already separates the two countries at the border between Tijuana and San Diego, but in San Diego's remote Border Field State Park a small fenced door known as the "Door of Hope" provides an opening in the barrier. Every weekend, U.S. Border Patrol agents open the passage to allow brief family reunions — and it has become a symbol of the immigration crisis. A Mexican border patrol agent named Arriaga insists that the area is a restricted zone forbidden to outsiders, despite its status as a symbol of reconciliation.

Change is coming to the border region with the election of Donald Trump, and no one has made this clearer than Brandon Judd, president of the National Border Patrol Council and avid Trump supporter. "Our leader has changed and so has the political climate, and now border patrol agents will stop enforcing Obama's policies and begin arresting more illegal immigrants," says Judd, who heads a union of 16,500 border agents. "This will please the new President and end the assault by illegal migrants on our southern border, who are trying to take advantage of the last few months before the new administration takes office to enter the country illegally."

Battle brewing

Even before the election result that shocked the world, it was clear the border patrol agents supported Trump. But in Democrat-dominated California, a struggle is brewing between local authorities and civil society on one side and the pro-Trump border agents on the other. Immigration is under the purview of the federal government, but officials in California have vowed to oppose Trump's plans by refusing to provide lists of illegal immigrants and continuing generous assistance policies to the undocumented. They are backed by numerous civil society organizations and the Catholic Church.

Approximately 750,000 young undocumented immigrants have benefited from the Deferred Action for Childhood Arrivals (DACA) program, a 2012 executive order signed by President Barack Obama that shields from deportation those who arrived in the country when they were children. More than 200,000 of them live in Los Angeles County, where Archbishop José Horacio Gómez has already declared he will not collaborate with deportations. Despite being a conservative nominated by Pope Benedict XVI in a country where most Catholics voted for Trump, Gómez's Mexican origins also inform his view on the issue.

"We need to build bridges, not walls," says Aida Bustos, spokesperson of the Archdiocese of San Diego. The city's Bishop Robert McElroy will hold a Christmas celebration on Dec. 10 at the border fence, "so Christians on both sides can pray together."

Bustos says she doubts Trump's immigration policy will be effective, for both moral and practical reasons. "We don't call immigrants illegals, they are our brothers in our Catholic family," she says. "I know hundreds of people here who have family members across the border, some who have papers and others who don't, so how will Trump be able to separate them?"

Antonio Marquez, who benefited from the DACA program is journalism student at San Diego City College, where Aida teaches. "I didn't violate any law or take advantage of the system, I've worked hard all my life to get into college and build my future," he says. "But now I have to live in fear because my parents took me to the U.S. when I was a kid, and at any moment the police could come knocking at my door."

Arrests and expulsions of undocumented immigrants are already at record highs, with 49,167 recorded in October. "The Casa del Migrante was founded to help those who were going from south to north, but now the flow has reversed and we receive around 30 deportees a day," says Fr. Patrick Murphy, the center's coordinator-general. "They used to come primarily from Mexico but now most are from El Salvador, Honduras, and Guatemala, and we recently had a huge influx of Haitians."

Murphy says the "root causes' of this historic migration should be addressed by improving conditions in migrants' home countries. "Otherwise, we'll never solve this problem," he says. "Fixing the symptoms of the crisis, like arresting criminals when they're just a minority, isn't going to work."

Cutting potatoes for lunch at the center's kitchen, Pina nods in agreement, saying he'll soon return to Matamoros, the city on the Rio Grande where he was born. "As soon as I have enough money I'll cross the river again," he says. "But please don't tell Trump, or he'll hang me."