Nogales (United States) (AFP) - Guadalupe Manrikez sums up the feeling of many in the small US border town of Nogales, when asked about Donald Trump's promise to build a giant wall dividing the country from Mexico.

"He is cuckoo," blurted out the 32-year-old Manrikez, who works at a perfume shop just steps away from the border between Arizona and Mexico.

The Republican presidential candidate's vow to build a "big, beautiful, powerful wall" -- and force Mexico to pay for it -- has been a centerpiece of his campaign.

But for many like Manrikez on the frontlines of America’s battle to curb illegal immigration, the idea elicits chuckles and is entirely implausible.

"This whole town is Mexican, all the families here are Mexican and everyone thinks he and his ideas are a joke," she told AFP, launching into a diatribe in Spanish against the billionaire businessman.

Many residents pointed to an 18-foot (5.5-meter) metal barrier that already separates Nogales from its sister city in Mexico as an example of why Trump's wall is unlikely to discourage migrants or drug smugglers headed to the US.

"We already have a wall here and people still manage to cross," said Adriana Ortega, an employee at a bridal dress shop that overlooks the border. "A lot of people manage to climb over the wall within sight of border patrol agents and don't even get caught.

"So the solution is not to build more fences, but to have more enforcement."

The barrier in Nogales, a town of some 21,000 mainly Hispanic residents living in the US legally, cuts across the downtown area and snakes into the desert hills surrounding the city on either side.

And like other towns scattered along the almost 2,000-mile (3,200-kilometer) US-Mexico frontier, the economy in the American side of Nogales is deeply intertwined with that of the Mexican part of the city.

"Most of the shops here rely on customers from Mexico," said Ortega, whose store features elaborate wedding gowns priced between $600 and $3,000. "And right now we are suffering because the economy in Mexico is down."

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- 'Wall won't stop them' -

A recent poll conducted by Spanish-language network Univision, the Dallas Morning News and Arizona State University's news channel showed that the overwhelming majority of residents in communities along both sides of the US-Mexico border -- 86 percent in Mexico and 72 percent in the US -- are opposed to the construction of a wall between their countries.

The majority also feel the tone of the presidential campaign could hurt relations with America's third-biggest goods trading partner.

Mexico is a key customer for the four border states of California, Arizona, New Mexico and Texas. Everything from cars, computers and machinery transit the border daily, and millions of jobs on both sides depend on that relationship.

For Irwin Perez, who works at a Mexican restaurant in Nogales that is popular with locals, including border patrol agents, Trump's anti-immigrant rhetoric harks back to a dark time in history.

"Even though he's not calling for Mexicans to be put in gas chambers or labor camps, he's still calling for families to be deported and these are people who pay taxes and have established roots in the US," Perez said, referring to the 11 million undocumented workers, many of them Mexican, who Trump has vowed to deport.

"These people are part of the US workforce, doing jobs that Americans won't even touch," added Perez, 26, who was born in the US to Mexican parents. "They are fleeing persecution in their country, poverty and even a 2,000-foot wall won't stop them.

"But sadly, Trump has already built so many walls just with his words."

- Ignore rhetoric -

Perez, like more than a dozen residents and business people interviewed in Nogales, said he has stopped paying attention to the inflammatory campaign talk and had little faith that Trump, or for that matter his Democratic rival Hillary Clinton, were committed to fixing a broken immigration system.

"I pretty much don't listen to anything they say anymore," said Javier Mayer, manager at a produce company that employs about 50 people, mainly Hispanics. "What Trump is proposing is logistically impossible.

"He can't kick every Mexican out of the country."