The immigration detention center known as “Ursula” occupies the corner of West Ursula Avenue and South 37th Street in McAllen, Texas, just south of the highway. The center, it is apparent, was not built to house people. It shares a nondescript street with ex-urban warehouse structures; its façade is composed of 30-foot walls of windowless beige-gray corrugated metal, extending roughly 200 feet across and 100 feet deep, making it a perfect place to store paper towels or de-icing salt. Ursula is surrounded by a chain-link fence with plastic inserts to conceal the view inside; barbed wire runs along the top. A trailer of mobile showers is parked outside. Several times a day, busses roll in empty and roll out full, headed downtown.

McAllen, which lies in the southern part of the Rio Grande Valley, has the distinction of being the 22nd largest city in Texas. It is about 350 miles southwest of Houston and 240 south of San Antonio, but its proximity to the Mexican border, across from Reynosa, has made it a center of the American immigration crisis. Since 2014, Central American asylum seekers have been crossing the border daily, by the hundreds, often turning McAllen into both a bureaucratic checkpoint, where immigrants are processed and detained, at least temporarily, and a terminal from which they head to points north, east, and west to meet family, reunite with loved ones, or try to make it on their own. Last month, in response to reports of a caravan of several thousand Central American asylum seekers headed north through Mexico, Donald Trump first raged at the migrants, then threatened their home countries, then campaigned on it, then announced he was sending about 5,000 military troops to the border to fend off the inundation.

Trump may have deployed the National Guard as a form of pre-midterm, narrative-rattling show of force, but those expecting a modern-day Green Zone in McAllen would be disappointed. When I visited in late October, the troops were undetectable—hidden, even. According to reports and local word of mouth, the guards would stay in rental apartments, because there were no barracks; they would wear civilian clothes, because residents didn’t want a war-zone vibe; and they would have no direct contact with migrants, because that would be legally fraught. So, what were they doing in McAllen, exactly? Chris Cabrera, a spokesman for a Border Patrol agents union, told me that the National Guard members have so far been doing things like helping to mind the cameras from which border agents direct colleagues in the field. But here, too, was a snag. “The National Guard guy doesn’t know what’s what or how to direct people there, because he’s never been here,” Cabrera said. “So the agent is sitting next to the National Guard guy watching the same camera.”

Almost independent of Washington, McAllen has transformed itself into a humming administrative machine for what critics call catch-and-release policy, a term for letting border crossers go shortly after being detained. Four years ago, immigration authorities didn’t know what to do with people getting out of detention, and simply dropped them at the city’s central bus station to figure it out. Then a nun named Norma Pimentel, or Sister Norma, the executive director of Catholic Charities’ regional operation, asked to help and found first one space, and then another, to shelter people temporarily while they figured out where they were going. Soon, Sister Norma was taking in hundreds of people a day. She is still taking in hundreds of people a day. Brenda Riojas, the group’s media intermediary, estimated the number to be around 500 a day. Others estimated 200 a day. Now, when a bus of released asylum seekers rolls out from Ursula to McAllen’s central station, volunteers from Sister Norma’s operation are on hand to greet them, sort them, and advise them. Border Patrol relies on them.