In Mexico it is known as “el efecto Trump”: a barrage of taunts and tweets that rattle the economy and hammer the peso. For the new president, it is part of a strategy to pressure companies to move jobs back to the United States. Mexico’s job will be to suck it up, accept the millions of people Trump has promised to deport, and pay for the proposed border wall.

Reality may soon disrupt this vision because Donald Trump, in one of the first great ironies of his presidency, has given impoverished Mexicans more reason to migrate to the US.

The peso’s slump against the dollar has dramatically driven up their cost of living, fuelling angry protests and steeling the resolve of some to sneak across the border.

“You’re going to see a lot more people from the south coming up here to cross,” said Paulino Hernández, 38, seated in a Catholic-run migrant shelter in Tijuana, on the border with California. “People are feeling bad. Everything has become so expensive. The dollar now goes a lot further.”

Hernández, a construction worker who has lived illegally in San Diego since 2000, recently visited relatives in Oaxaca, in southern Mexico, and found young people clamouring to join him on his trip back to the US. “They want to go north.”

Trump stormed into the White House on vows to end an “invasion” of “illegals”, deport millions of undocumented immigrants, and seal the border.

The numbers trekking north had dwindled over the past decade as the Mexican economy improved, and the US economy struggled, but the mood now was bleak, and dreams of life in the US glowed anew, Hernández said. “My nephew begged to come with me. He doesn’t see a future in Mexico.”

Mexico’s former president Felipe Calderón recently tweeted a warning to America’s new president: “The more jobs you destroy in Mexico, the more immigrants the American people will have. Think a little!”

Gordon Hanson, a UC San Diego economics professor who studies migration trends, said Trump had reversed the macro-economic climate and created uncertainty about Mexico’s future. “Greater instability could induce younger workers … to start their careers in the US. It does ironically increase the incentive to move north. Everything we’re seeing now is the Trump effect.”

Trump’s victory over Hillary Clinton jolted an economy left vulnerable by anaemic growth and faltering reforms. The peso swooned from 18 to the dollar to 20 in the election’s immediate aftermath and slid again to 22 in recent days as Trump ratcheted up the pressure.

He threw Mexico’s car industry – a sizable employer –into disarray by threatening Ford, Toyota, General Motors and other manufacturers with tariffs unless they shipped jobs to the US. Ford denied any connection but announced the cancellation of a planned $1.6bn (£1.3bn) plant in Villa de Reyes, saying it would expand a facility in Michigan. Trump greeted the move as “just the beginning”.

The president has also threatened to renegotiate trade terms, which sustain thousands of factories known as maquiladoras along Mexico’s border. And to swipe remittances, money that immigrants in the US send to relatives in Mexico – a multibillion-dollar lifeline – to fund the wall.

“Every time he says something, the peso weakens against the dollar,” the El Mexicano newspaper lamented in an editorial after Trump’s press conference last week. “From those words, there are already results, a new blow against the Mexican economy.”

Frustration boiled over this month, after gasoline prices jumped 20% in the wake of energy deregulation. The “gasolinazo” will have a knock-on effect on the price of food and public transport. Protesters marched in cities across Mexico and blockaded some border crossings.

“I barely earn enough to eat,” said Óscar Rosas, 40, who earns the equivalent of $8 a day washing cars in Tijuana. He sleeps in a friend’s car and wears donated, stained clothes. He yearns to cross the border fence and return to Los Angeles, home for 15 years until he was deported last year. “Life is so much better there. Easier.”

Traditionally, migrants delay travel to spend Christmas at home, with numbers rising from late January.

Any surge would probably be modest compared with the influxes of the 1990s. Fertility rates have plunged, so there are far fewer young people. And border security has tightened, making the crossing expensive – $7,000 is a common figure touted by smugglers – and perilous, a gauntlet of thieves and kidnappers, fierce temperatures and terrain, with only a 50/50 chance of eluding the border patrol checkpoints, sensors, cameras and aircraft.

However, even a small uptick could reverse what was arguably the most overlooked fact of the presidential election: the Mexican influx has become a net outflow – more Mexicans are leaving the US than entering.

“It would be an interesting effect of an attempt to reduce migrant flows across the border,” said Mark Hugo Lopez, of the Pew Research Center. It would not all be due to Trump. “Mexico’s own decisions are perhaps setting the stage for a growing migration trend north as gas price controls have been relaxed.”

The peso’s weakness made a dollar income all the more alluring, said Hanson, the analyst. “I’d say in the short turn you’ll certainly see increased pressures for migration.” In the long run, those pressures could abate as Mexico’s economy adjusted, especially if Trump’s threats proved to be largely bluster, Hanson said. But if the president did overturn the economic order “you don’t know what comes next”.

Father Pat Murphy, a Catholic priest who runs a migrant shelter in Tijuana, said a major concern was the US taxing remittances to help fund the wall. “That money is what holds people together here. If that gets cut it’ll be another slap in the face of Mexico.”

In previous eras, undocumented migrants used to return to Mexico for weddings, funerals and Christmas, then slip back into the US. With border crossing now so fraught, fewer risk it.

Hernández regrets leaving his wife and children in San Diego to visit his mother and siblings in Oaxaca. Last week, purported coyotes – people-smugglers – kidnapped him and demanded a ransom from his wife. The former soldier escaped but lost his cash, phone and confidence about crossing.

If Trump further bolsters security with his “big beautiful wall”, undocumented immigrants will have all the more reason to never leave the US, he said. “If you get in, stay in.”