The candidates for president of the United States, particularly on the Republican side, have hotly debated how to handle the roughly 2,000-mile (3,200-kilometer) border between the United States and Mexico.

Donald Trump has famously and repeatedly promised to seal the border with a wall if he's elected. He and others have promised to send people who illegally crossed the border—a number that appears to have leveled off—back to Mexico. For these people, the border wall isn't an abstraction. Many parts of the border are already covered in fences. In other spots, the wall is not made of bricks, but out of scanners, drones, and guards.

Photographer James Whitlow Delano has visited the border several times in the past decades as these walls have gone up. These are his photos and stories:

In the photo above, the border wall separates Jacumba, California, from Jacume, Mexico, in the high desert. Even after the first border barricade was built here in the mid-1990s to disrupt human and drug traffickers, residents of Jacume could cross freely into Jacumba to buy groceries or to work, and children would be brought across to go to school or to the health clinic. Since September 11, 2001, security has turned a ten-minute walk into a two-hour drive through the official border crossing in Tecate, segregating these communities from each other. After ten years, Jacume, a village of 600, was called "a black hole," where even Mexican federal agents had been held hostage for attempting to extort money from smugglers.

A double border wall near San Diego blocks undocumented migrants from using the Tijuana River—located on the other side of the second fence—as a corridor into the U.S. In the 1980s, entire families would rush across the border, believing more of them would get through the gauntlet if the U.S. Border Patrol was overwhelmed. Here, in the 1980s, I watched waves of frightened Mexican families, young and old, run through, trying to evade Border Patrol agents and, at times, risking life and limb by crossing a busy freeway nearby. This wall put an end to the runs.

When I first visited this spot in San Diego, where the border meets the Pacific Ocean, in 1982, there was a single corrugated steel wall that ended at the top of the beach. Helicopters circled above, but it was still physically possible to walk straight into Mexico or vice-versa. At the very end of the wall, on the Tijuana side, someone had spray painted "sin fronteras" ("without borders"). Now the wall extends into the breaking waves.

This lonely stretch of border is known for banditry.

For all the talk of sealing the border, this valley about 19 miles (30 kilometers) from the Pacific Ocean has no wall at all. From the U.S. side, it's forbidden to go any farther than the gate seen in the lower right, but the gate is the only physical barrier.

View Images

A parked U.S. Border Patrol vehicle looks out across the border wall at Tecate, Mexico, a city famous for Tecate and Carta Blanca beers. As is typical along the border, the city on the Mexico side pushes all the way to the wall, while the U.S. side is largely open country.

Yellow smoke rises from a brush fire south of the border wall in the Sonoran Desert, where California, Arizona, and Mexico meet. The increased surveillance near Tijuana and the coast pushed migrants eastward, where there were fewer U.S. Border Patrol agents.

The U.S. government filled in Smuggler's Gulch with a structure resembling an earthen dam and built a triple-thickness border fence topped with razor wire, flood lights, remote sensors, and cameras to deter nighttime crossings.

For decades, traffickers would smuggle everything—cattle, people, moonshine, cocaine—through this canyon, making it one of the most treacherous places along the border. In the 1990s, Smuggler's Gulch was a prime route for undocumented migrants attempting to enter the United States.

The Smuggler's Gulch fence is part of a 60-million-dollar project to install triple fencing over the final 3.5 mile (5.6 kilometers) of fence between San Diego and Tijuana.

The border fence ends and is replaced by a barrier on a desert plain in the Imperial Valley, at the edge of the irrigated oasis farmland west of Calexico. Border patrols were completely absent here, as opposed to all other places I visited along the border. Elsewhere, Border Patrol agents regularly approached to determine my nationality and to ask why I was so close to the line. Here, there was nothing but solitude.

This wall separates Calexico, California from Mexicali, Mexico. As their names imply, the two are sister cities, and the wall was not always this big. In the 1980s, there was a rickety corrugated steel wall that didn't even extend to the edge of the cities. But in 2008, when I visited again, U.S. crews were extending and reinforcing the barrier. Mexicali has a notorious reputation, but there were prosperous suburbs south of the city, complete with shopping malls and Starbucks.

That said, Mexican cartel violence has been known to spill over the border because of the lucrative smuggling business. In April 2015, U.S. Border Patrol agents seized more than 69 pounds of methamphetamine coming over the border. In the process, they found how smugglers were getting around the wall between Calexico and Mexicali—they had built a tunnel.