And yet, the closer you get to the border, the fewer people think that it might work — even among Trump supporters and law enforcement officials. “The wall is a fantasy,” said Tony Estrada, the sheriff of Santa Cruz County, Ariz., a border district that is one of the busiest corridors of drugs and people smuggling in America. “I don’t care how big, how high or how long it is — it’s not going to solve the problem.”
He sighed. “But people are eating it up,’’ he said. “I can’t believe it.”
Mr. Estrada, who is 73, knows better than most that borders are more than lines on a map. Born in Mexico, he arrived in America at the age of 1. Until the 1970s, he said, the border had an organic quality. During the Cinco de Mayo fiesta, dancers paraded from Mexico into America then back again; beauty queens from both countries sat together on a platform that straddled the border; white tourists crossed into Mexico for the bullfights, the night life and the “rum runs” — cheap alcohol.
Then the drug wars exploded, and in 1995, a fence started to rise. Crime fell sharply, but the drop exacted a cost. Tourism withered, the curio shops closed and there was a painful tear in the cross-border culture. “The dynamic changed,” he said.
The sheriff’s nostalgia pointed to a wider truth: Walls are not just about whom a country wants to keep out; they are a mark of what it is trying to preserve, its idea of itself. With the rise of Mr. Trump, America’s sense of itself is suddenly less sure. And so I spent a week in the southern borderlands, flitting between Mexico and America, trying to figure out what, in this febrile election season, that idea might be.
The fence itself is a formidable sight, spanning about one-third of the 2,000-mile frontier from California to Texas, and patrolled by about 20,000 agents. One of the most tightly guarded stretches is around the city of Nogales, which straddles the border. Here, the first world abuts the third. American Nogales, orderly and somniferous, pushes up against Mexican Nogales, an unruly metropolis of 300,000 souls where the Sinaloa cartel looms large.
John Lawson, a border patrol officer born in Pennsylvania, took us on a tour of the fence, a slatted metal barrier, 18 to 30 feet high, that undulates along the hills on either side of Nogales. It was built at a cost of $4 million per mile, which includes an array of military-style fortifications. We passed pole-mounted cameras, radars, vibration sensors and, in the dip of valley, a line of World War II-style Normandy barriers meant to stop any Mexican vehicle from crashing through America’s front gate. The border patrol reaches into the air, too, with a fleet of drones, balloons and Blackhawk helicopters.
And yet, the “migrantes” and the “traficantes” still slip through.
Officer Lawson pulled up on a small bluff overlooking the border and pulled out his binoculars. Half a mile away, inside Mexico, three young men trudged along a ridge, then vanished behind a splash of foliage. Farther along we saw other groups: spotters, employed by the cartel, Officer Lawson said. They use their cellphones to direct traffic, telling migrants and drug smugglers when to make a run for it. Looking left and right, on the American side, I counted six patrol jeeps, parked on hillocks.
Both sides sat still, watching the other, waiting for one to make a move. “The purpose of the fence is to buy time,” said Officer Lawson. “It allows us to respond. But it can’t stop them completely. Nothing can.”
As in Europe, where rising walls have forced migrants to chance their lives in rickety boats, the militarized American border has created ever more perilous routes. In Arizona, that means heading for the desert. Beyond Nogales, where the fence peters out, migrants march for days through a sweltering landscape. Since 1999, more than 2,000 people have died in the Arizona deserts, often from exhaustion or thirst, according to the Tucson Samaritans.
Before setting off, many migrants pass through the comedor, a tin-roof shelter within sight of the border in Nogales, Mexico. The staff of the charity offers food, legal advice, massages and small compasses to help those who might get lost in the desert. Hope mingles with heartbreak along the cramped benches where breakfast is served. Men like Mr. Talavera, plotting a way to the United States, break bread with families that have just been deported, their faces etched with dejection. Under President Obama, the United States has deported 2.5 million people — more than any other administration.
The comedor is named after Eusebio Kino, an Italian Jesuit who roamed these lands in the early 18th century, and its staff members are driven by their own sense of mission. The morning we visited, a Catholic nun delivered a cautionary lecture about José Antonio Elena Rodríguez, a 16-year-old Mexican shot dead through the fence by an American patrol agent in 2010 (the agent was charged with murder this year). A priest offered a blessing and the men filed out.
Walking in twos and threes for safety, they melted into the streets, biding their time to make a break for the border.
In Arizona, the sweeping landscape is dotted with relics of the Old West. In the town of Tombstone, tourists pay to see a comical re-enactment of the shootout at O.K. Corral. Farther out, in Skeleton Canyon, a roadside monument marks the surrender of the great Apache warrior Geronimo in 1886 — a reminder of the Native Americans who once held sway here.
To modern-day cowboys and ranchers, Mexican migrants are the new foe. Ranching families thronged to the Cochise County Fair, outside the border town of Douglas, for an archetypal show of rural Americana. Children screamed with delight at the turkey race as their parents went to the rodeo; neon-lit stalls sold corn dogs, Confederate flags and gun paraphernalia.
Tony Fraze, a rancher and Trump supporter, paused to chat. Migrants were the scourge of the area, he said. They damaged fences, vandalized water systems and left trash that killed livestock. “You can’t leave your door open or your keys in your truck,” he said. “If you do, they might take them and kill you, too.” He mentioned Rob Krentz, a local rancher shot in 2010 in a traumatic case that briefly made the national news.
Although he was right on the specifics, the border counties generally enjoy some of the lowest crime rates in Arizona. As Sheriff Estrada told me, smugglers don’t like to court trouble. “They’re businessmen, and confrontation is bad for business,” he said.
But to Mr. Fraze, it was about more than just the border: Weakness on immigration mirrored a broader decline of American strength. “We’ve had too much wishy-washy — people trying to control it, not end it,” he said of migration policy. “That’s what we should have done years ago with the World Trade Center — flown over there, put it back to nature and have it done. Playin’ around just don’t get it done.”