If the Trump administration follows through on veiled hints that it’s considering cutting foreign aid to Mexico, it could shut down a program that blocks hundreds of thousands of immigrants at Mexico’s southern border—keeping them from eventually entering the United States. That’s according to a report put together by Congress’s in-house think tank and obtained by The Daily Beast.

Buried in Trump’s recent executive order on immigration is a section ordering the heads of federal agencies to figure out how much foreign aid and assistance the U.S. sends to Mexico every year. It’s widely speculated that this provision was included as a first step toward cutting aid to Mexico—and then using that money to have Mexico “pay for” Trump’s much-promised border wall.

But eliminating that aid could undercut Trump’s stated goal of reducing the number of undocumented immigrants who enter the U.S. every year. The report obtained by The Daily Beast shows that the bulk of U.S. aid to Mexico funds the so-called Mérida Initiative, which helps bankroll Mexico’s own Trump-esque border policy—one that turns away Central American immigrants by the hundreds of thousands.

If Trump wants a southern barrier against asylum-seekers, he already has one. Under the Mérida Initiative, the government of the U.S. pressures Mexico to turn away Central American immigrants before they reach the U.S. While immigration from Mexico to the U.S. has largely been static for years, border hawks in the U.S. point to a recent uptick in illegal immigration from three Central American countries—Honduras, El Salvador, and Guatemala—as evidence that the federal government needs to implement stricter border policies. But if Trump makes good on threats to cut funding to Mexico in exchange for his border wall, his anti-immigrant fight could just move one border closer.

“A substantial piece of the Mérida Initiative in recent years has gone toward strengthening Mexico’s southern border,” Lisa Haugaard, executive director of the Latin America Working Group, told The Daily Beast. “The Obama administration in recent years put significant pressure on Mexico to step up its southern border and the deportation of Central Americans.”

The Congressional Research Service report that The Daily Beast obtained shows that the U.S. gave $100 million in fiscal year 2016 to the Mexican government to fund the Mérida Initiative as part of the State Department’s support for international narcotics control and law enforcement.

Critics say the U.S. government uses these funds to push the Mexican government to send migrants with legitimate asylum claims back to their violent home countries.

“Mexico was deporting Central Americans, many of whom had valid asylum claims because they were fleeing violence,” Haugaard said, adding that Mexico has been “bending over backwards” to meet the American government’s demands.

Haugaard said these U.S.-aided efforts on Mexico’s southern border helped fund hundreds of thousands of deportations, often returning immigrants to violent nations before they could apply for refugee status or reach America’s southern border.

“In 2015, Mexico apprehended nearly 172,000 migrants who came from the ‘northern triangle’ [El Salvador, Honduras, and Guatemala] of Central America. In 2016, Mexico apprehended another 153,000 migrants from Northern Triangle countries,” and tens of thousands from other countries, the CRS report reads.

“I think right now the emphasis of Trump’s policy on immigration, the general recognition within Washington’s policy-making community, is that Mexican immigration has significantly slowed down,” said Ana Quintana, a policy analyst focused on Latin America and the Western Hemisphere at the conservative Heritage Foundation. “What we’re seeing the ramp-up of is from Central America.”

According to the CRS report, the U.S. gave the Mexican government a total of $161.2 million in FY 2016. Trump’s wall, meanwhile, would cost $12 billion to $15 billion, according to a January estimate from Senate Majority Leader Mitch McConnell. The actual figures, some scientists say, will run much higher. A study by the MIT Technology Review concluded that, even if the wall only covered half of the 2,000-mile border, the project would cost $40 billion, not including mile-high maintenance costs.

And despite Trump’s campaign promise that Mexico would pay for the wall, his administration has yet to outline a concrete funding plan, instead suggesting a series of policies that would put the burden on Mexican immigrants or American consumers. In April 2016, Trump sent The Washington Post a two-page memo promising that, if elected, he would demand Mexico “make a one-time payment of $5 to $10 billion” or he would cut off money transfers between U.S.-based Mexican immigrants and their families in Mexico, which account for some $25 billion annually. He has also suggested imposing fees on visas and green cards for Mexican immigrants, or imposing a 20 percent tariff on Mexican imports.

Mexican leaders have flatly denied the country will pay for the wall. On Jan. 25, on the eve of a planned meeting with Trump, Mexican President Enrique Peña Nieto reiterated that Mexico “will not pay for any wall.”

“If Mexico is unwilling to pay for the badly needed wall, then it would be better to cancel the upcoming meeting,” Trump wrote the following morning.

Later that day, Peña Nieto canceled. The pair spoke on the phone the following morning and reportedly agreed not to address their dispute in public.

Facing his own low approval ratings, Peña Nieto’s dealings with Trump could determine his political future.

“President Peña Nieto’s approval rating has remained extremely low (under 25 percent) since 2014,” the CRS report reads. “Peña Nieto may have limited room to maneuver in future negotiations with the Trump administration, as Mexican legislators and businesspeople are urging him to more vigorously defend Mexican interests.”

If Peña Nieto is seen as weak in negotiations with Trump, support could swing toward political opponent Andrés Manuel López Obrador, “a leftist populist who is unafraid to antagonize the United States, in Mexico’s 2018 elections,” the CRS report reads.

Quintana said she expects the Trump administration to keep funding immigration enforcement efforts on Mexico’s southern border.

“I think it’s in both countries’ interests to not let things escalate beyond this point,” she told The Daily Beast.