In December, the Mexican migration authority said it had run out of money and stopped deporting migrants moving through the country. It also stopped flying them from Mexico’s northern border to the interior of the country. Coincidentally, perhaps, migrant encounters with U.S. agents at the border with Mexico surged over 300,000, the highest monthly tally on record.

Homeland Security Secretary Alejandro Mayorkas and Secretary of State Antony Blinken had barely returned from Christmas break when they were dispatched to plead with Mexican President Andrés Manuel López Obrador on Dec. 27. And on the 30th, the Mexican government found the cash to start moving migrants away from the U.S. border again.

AMLO, as the Mexican president is known, took the opportunity to lay down some demands: an end to the Cuba embargo, removal of all U.S. sanctions against Venezuela, the legalization of some 10 million unauthorized immigrants living in the United States, and $20 billion for countries in the region. He forgot to ask for a unicorn.

Still, Washington exhaled: In January, migrant encounters with the U.S. Border Patrol plunged.

President Biden’s caution with his demanding counterpart south of the border has been, let’s say, uncharacteristic for the United States. Washington has said next to nothing about López Obrador’s campaign to dismantle the institutions underpinning Mexico’s young democracy or anything about the military’s encroachment on civilian life. Issues of direct national importance — the flow of fentanyl over the border, Mexico’s nationalist energy policy likely in breach of agreements with the United States — have elicited little more than a polite suggestion from Washington to reconsider.

The reason, of course, is immigration: AMLO finds himself in control of the most powerful political narrative in Washington, one that could determine the presidential election in November.

As presidential elections approach in both Mexico (June) and the United States (November), some Mexican critics are voicing concerns that AMLO might be playing with the migration valve to warn Washington about the potential consequences of saying anything mean about his, say, questionable tactics to ensure a win for his handpicked successor, Claudia Sheinbaum.

It’s not unreasonable for Washington to fear AMLO might be willing to play with the migration valve to favor Donald Trump, for whom the Mexican president has expressed some inexplicable affinity. Few things would hurt Biden more than an October migration surprise.

“Mexico’s changes in migration policy have an inevitable political impact in the U.S.,” noted Tonatiuh Guillén López, who headed Mexico’s National Institute of Migration in the early years of López Obrador’s administration. “It would be innocent to think Mexico doesn’t know this.”

In 2022, Mexico returned, on average, more than 10,000 migrants per month to the countries of their origin. In 2023, the average dropped to 4,500, less than 7 percent of migrants encountered by the authorities. In December, Mexico returned only 378.

Whatever López Obrador is thinking, though, Biden’s vulnerability to Mexico’s migration policies is Washington’s own fault — a predictable consequence of outsourcing migration control to Mexico. It is hardly crazy that Mexico’s president would deploy what leverage he has to ensure some favorable political outcome. The United States has played that game for years. What is preposterous is that the U.S. political system (here’s looking at you, Speaker Mike Johnson) would expose the United States to this kind of manipulation.

Biden is to be commended for refraining from using the hardball tactics of his predecessor, who threatened Mexico with tariffs unless it kept Central American migrants south of the border. But Biden failed to do anything else, perhaps believing that goodwill would seal a deal on its own.

Cruel as it may seem, migrants make for powerful weapons. Think of the Mariel boatlift of 1980, when Fidel Castro opened the door for an exodus of disillusioned Cubans toward Miami, partly to get rid of them and partly to buy leverage with President Jimmy Carter.

President Nicolás Maduro has tried to extract political gain from millions of desperate Venezuelans fleeing oppression and destitution, many hoping to make a life in the United States. President Daniel Ortega opened Nicaragua to serve as a transit point for hundreds of thousands of migrants hoping to reach the United States from as far away as former Soviet republics, mainly to poke Washington in the eye.

While there is no obvious fix, there are a few things Washington could do to meet the moment. Number one would be to ensure the swift processing of asylum applications. This alone would establish that the United States will offer safe harbor to those who need it while dispelling the idea, held by many migrants across the hemisphere, that asylum offers an open door to everybody.

Washington should also reconsider limits on work-related visas, opening a wider door for migrants seeking a more prosperous life. Critically, it should engage with neighboring countries to share the burden — and the opportunity — carried by hundreds of thousands of migrants moving to improve their lot wherever they land.

While the United States reconsiders its immigration policy, it might also make sense for Mexico to think hard about its goals and strategy. Donald Trump benefits from the immigration mess — so much so that he single-handedly turned House Republicans against bipartisan legislation that took a small step toward establishing order at the border. He would be delighted by an October migration surprise.

AMLO might very well like that too. Trump’s no-nonsense transactional style seems to suit him. Both share an undisguised contempt for democratic institutions constraining their power. Democrats may remember President López Obrador’s words to President Trump soon after winning the Mexican election in June 2018: “We managed to put our voters and citizens at the center and displace the political establishment.” The “establishment” was them.

From where I sit, though, another Trump administration, complete with arbitrary import tariffs, mass deportations and concentration camps for migrants, looks like a disaster for Mexico. Whomever Mexicans elect come June — AMLO’s chosen candidate Sheinbaum looks like the lucky one — would have to live with the consequences.

There is an old analysis sitting in the CIA archives that notes Castro stopped the Mariel exodus when he saw the political damage it inflicted on Carter and the boost it gave to the candidacy of Ronald Reagan, “who is viewed with grim foreboding in Havana.” It was too late. Reagan won. And the 125,000 Cubans that made their way to Miami turned Florida, and American politics, even more hostile toward the island.

Sheinbaum might want to have a conversation with her patron about the substantial risks that can flow from the migration authority running out of money.