CALEXICO, Calif. -- It looks like the perfect scene for a Donald Trump commercial:

A constant stream of Mexican citizens swiftly pass through metal turnstiles at a border crossing as they head back home. In the background looms an imposing steel fence.

But it's not what it seems. It's just quitting time in Calexico, Calif., a windswept border town dependent on Mexican workers and shoppers to survive.

As Trump continues to ride anxiety about illegal immigration all the way to the Republican presidential nomination, his call to fortify the entire U.S.-Mexico border with "a beautiful" prefab-concrete wall _ at least 30-feet tall _ is scaring some of the people he says he's trying to protect.

The wall has burnished Trump's credentials nationally with law-and-order Republicans and snagged him the endorsement of the union representing Border Patrol agents. But it's a divisive issue for those who would actually have to stare at it every day, pitting residents with legitimate security concerns against those whose livelihoods depend on continued economic integration with Mexico.

The mixed opinions on Trump's wall depend mostly on what people see when they look across the existing border fence.

Mark Holloway, a Republican and the third-generation owner of a Calexico clothing store, sees Mexicali, a Mexican metropolis where 95 percent of his customers live. "Anybody who lives in Calexico would be anti-wall," he said. "Without the Mexican consumer, we wouldn't be here."

About 50 miles to the west, however, rancher Robert Maupin, who keeps a .40-caliber Glock handgun fastened to his hip, looks out at the rolling hills of sage brush he says are controlled by Mexican drug cartels.

"It's like living in a bad neighborhood that's run by a drug gang," said Maupin, a fan of Trump and his wall. "When your wife and your kid have to go out of their house armed and fearful for their life, what kind of life is that?"

California's 137-mile border with Mexico doesn't resemble the no man's land Trump paints in his stump speech.

Although much of the U.S.-Mexico border in Texas, Arizona and New Mexico remains wide open to migrants and smugglers alike, 85 percent of California's border is fenced _ three layers thick in some areas around San Diego. One stretch of the fence even extends into the Pacific Ocean to prevent migrants from swimming into the U.S.

The American side of the border is barely more politically hospitable to Trump than the Mexican side. Other than Imperial Beach, a military town south of San Diego, it's mostly Latino and Democratic.

As for the Republicans, many admire Trump's bravado and business success; but they laugh at the wall.

"It's never going to work," said Holloway, whose clothing store is a block from the border. "I'm here every day. I've seen them with pulley systems. I've seen them with ropes. They're too creative. Just take a look at the tunnels they've been finding here."

Juan Hidalgo, a Republican running for Congress in a district that hugs the border, is anti-wall. So is Brian Bilbray, a former Republican congressman from Imperial Beach.

"Trump doesn't have a clue about the border," Bilbray said. "Calling immigration a border problem is as absurd as calling a heart attack a shoulder problem."

Bilbray credits his former House colleague, Duncan Hunter Sr., with pushing through legislation to build sections of the border fence, which stand between 6 and 18 feet tall. Most of the remaining unfenced areas are along mountainous regions that present their own obstacles to migrants.

Bilbray said the fence has done its job in helping to reduce smugglers and migrants.

Last year, U.S. Customs and Border Protection agents apprehended 39,110 people along California's border with Mexico. Twenty years earlier they apprehended 561,548 _ more people than live in Fresno, the state's fifth largest city.

For the most part, Calexico and the rest of California's sparsely populated Imperial Valley, two hours east of San Diego, functions as an appendage of Mexicali, a city of nearly 700,000 residents. The recent decline in the value of the peso, has further imperiled discount stores in downtown Calexico. The region's unemployment rate hovers around 20 percent.

"We're probably more closely allied with Baja than we are with California," said Sam Couchman, a Republican councilman in nearby Brawley who used to run the county's economic development department.

Many of his co-workers were Mexican nationals. "We get a lot of computer technicians and engineers coming from Mexicali," he said. "We can't attract highly educated people from the U.S. to come and work in the Imperial Valley, but we can attract highly educated Mexicans."

A giant concrete wall wouldn't stop workers from crossing at Calexico's border gate. But, Couchman said, the optics would be terrible.

"Symbolically,'' he said, "the message I would get if I were a Mexican citizen is that I am not wanted here."

But Maupin, the rancher, isn't shy about letting Mexican migrants and smugglers know they aren't welcome to pass through his sprawling property in the tiny town of Boulevard.

"If you can read this, you're in range," one sign on his property reads.

Maupin said the flow of migrants has dwindled from the 1990s, when as many as 20 a night would hop over or slip through his fence.

Trump's wall, he said, would make things even better and put an end to smugglers cutting though or going over the current fences.

"It's not only a good idea," he said, "it's necessary."

Whether it happens is another matter. But, even if it doesn't, Maupin plans on holding his ground.

"The only people who have ever offered to buy this place are working for the cartel," he said. "But I refuse to sell to them. I'm just an ornery bastard."