The tycoon-turned-politician has though given a sliver of detail about the "beautiful" wall he says he would build along the 1,989 mile border . Mexico, he says, would pay for its construction or else Mexicans in the US would be prevented from sending money back to their families. A Trump White House would "impound all remittance payments derived from illegal wages," according to the presidential contender's website . That is no small threat - remittances from all Mexicans abroad were worth $24.8bn in 2015 according to the Bank of Mexico , more than the country's oil revenues - but could it be done? "Is Trump going to steal the money," asks the former president of Mexico, Vicente Fox Quesada, incredulously. "How can any human being think like that? It's incredible! "It's not going to happen," he tells the BBC. "Forget it. We're not going to pay for that [expletive] wall!" This sentiment is echoed in Tijuana itself, often in similarly robust language. Mr Trump's description of Mexican immigrants as killers and rapists hasn't done much for his popularity here - an ugly mural with the caption "Rape Trump" adorns the border wall on the southern side - and in the colourful markets where Trump piñatas (papier mache effigies filled with sweets which children whack open at birthday parties) are selling like hot tacos, they have a wary eye on the superpower nextdoor. Beating the American businessman with a stick is popular, it seems. "People are worried by everything he's saying about Mexico and Mexicans," says Carmen Espinoza, in Spanish, behind the counter of her shop which has just one Trump piñata left. "We're not criminals, we're nothing like that. We are hardworking people who simply want to find work. Don't vote for him!" Of course some Mexican immigrants are criminals and in the past few years many have faced deportation from the US. In fact, President Barack Obama has reportedly deported more illegal immigrants than any president before him, although critics say that number has fallen sharply during his second term. As a result, across Tijuana we find what could be the scene from another Donald Trump dream - a room full of freshly deported "illegals". In this half-way house for new arrivals - the Casa del Migrante, a Christian mission which offers shelter, legal advice and psychological support - they're serving dinner. For some of the men and women here this is the first real taste of Mexico since they were children.

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