Rising GOP support for the U.S. taking unilateral military action in Mexico against drug cartels is increasingly rattling people on both sides of the border who worry talk of an attack is getting normalized.

Wednesday’s Republican presidential primary debate featured high-stakes policy disagreements on a range of issues from abortion to the environment — but found near-unanimous consensus on the idea of using American military force to fight drug smuggling and migration.

Florida Gov. Ron DeSantis made the strongest pledge on the stage with his response to Fox News moderator Martha MacCallum’s question asked whether he would support sending U.S. special forces into Mexico to “take out fentanyl labs, to take out drug cartel operations.”

“Yes. And I will do it on day one,” said DeSantis.

The governor’s eagerness reflects a growing normalization of the idea, which Republicans have embraced from the campaign trail to the halls of Congress.

Even more moderate GOP candidates such as former United Nations Ambassador Nikki Haley and South Carolina Sen. Tim Scott have suggested support for some version of unilateral military action across the Rio Grande.

Former President Trump’s hawkish approach to the bilateral relationship has led the way in mainstreaming the idea. As president, he sought Pentagon advice on launching missiles into Mexico, according to “A Sacred Oath,” a memoir by former Defense Secretary Mark Esper.

Esper talked Trump down, but the proposal still casts a shadow on U.S.-Mexico relations.

“I believe any action that is unilateral by the United States vis-à-vis Mexico, especially by U.S. uniformed forces, be they police or military, would be completely counterproductive to United States-Mexico relations,” said John Negroponte, who served as permanent representative to the U.N. under President George W. Bush and as ambassador to Mexico under Presidents George H.W. Bush and Bill Clinton.

“Mexico is our largest trading partner. We share a 2,200-mile border and we have inter-relationships that are extensive and across an entire spectrum of issues such as migration, trade, people-to-people relations and environmental concerns. I believe such action would be extremely ill-advised,” Negroponte said.

Over the past century, bilateral relations have eased from the brink of war to deep collaboration on that catalog of issues, though many in Mexico remain distrustful of U.S. influence.

The last major U.S. military intervention in Mexico ended in 1917, as the latter country’s revolution entered its final phase. Known then as the “punitive expedition,” the mission led by Gen. John Pershing saw 10,000 U.S. combatants deployed to northern Mexico over the better part of a year.

Better commercial and cross-border relations came with decades of political stability in Mexico, culminating in the signature of the North American Free Trade Agreement (NAFTA) in 1992.

While cooperation has only intensified since then, open and direct collaboration between U.S. and Mexican security forces remains elusive; the Pentagon’s long-term goal of better integration with the Mexican military hit a speed bump amid Trump-related tensions.

But a century of progress could be erased overnight, a Mexican official told The Hill.

“Any military intervention in Mexico would be a monumental setback for the U.S. and would derail the bilateral relationship. It can destroy the North American trading bloc and worsen the security situation, triggering a wave of migration in the region.”

Now, bilateral tensions are being stimulated on both sides of the border, with Mexican President Andrés Manuel López Obrador pursuing an internal image of defiance against the United States.

“It’s been made worse obviously in the process by President López Obrador’s denial of Mexico’s role in fentanyl trafficking — the fact that he says that fentanyl isn’t produced in Mexico — which is absurd because its own armed forces parade seizures of labs and of fentanyl being produced in Mexico,” said Arturo Sarukhán, who served as Mexican ambassador to the United States from 2007-13.

“In many ways, López Obrador unwittingly has fanned the flames of anger, vis-à-vis Mexican positions on law enforcement collaboration, so it’s the perfect storm.”

Despite the political pressures that driven in part by a frantic search for solutions to the opioid epidemic, a few cooler heads remain.

On the debate stage Wednesday, former Arkansas Gov. Asa Hutchinson (R) opposed the unilateral use of U.S. military or police force in Mexico, harkening back to his experience as head of the Drug Enforcement Administration.

“We cannot be successful against the cartel unless we bring in Mexico as a partner. We have to use economic pressure to accomplish that,” said Hutchinson, though he added that López Obrador “has not been helpful.”

Former Vice President Mike Pence lauded Hutchinson’s appeal for economic pressure, but said he would “engage Mexico the exact same way” as the Trump administration to ensure security cooperation.

Hutchinson, who also served as the top border security official when the Department of Homeland Security was created in 2003, was more channeling the approach of the pre-Trump GOP.

“​​What Hutchinson said last night is a clear reminder of the way the GOP would go about addressing issues of transnational collaboration in the fight against transnational organized crime with countries like Mexico,” said Sarukhán.

But the post-Trump GOP, according to its opponents, is a ticking time bomb.

“I think what you’re seeing is the unraveling of a political party in real time,” said Texas Rep. Joaquín Castro, the top Democrat on the House Foreign Affairs Western Hemisphere Subcommittee.

The idea of unilateral military action is a placeholder for a lack of policy proposals in other fields, said Castro, but he warned the idea is already snowballing.

“What happens is, somebody popular in their party starts talking about it, and then the other candidates start parroting it. And after time, their base takes it on as a core idea and gets behind it.

“And then the base starts demanding that every Republican in the country, whether they’re running for president or school board, agrees with this idea. And that’s the evolution of this whole thing. And that’s what’s gonna happen here. If something doesn’t change, that’s what’s gonna happen here.”

Pressed for further comment on DeSantis’s hard-line position, his campaign said “he will do what is necessary to stop the deadly flow of Fentanyl and other narcotics from the Mexican drug cartels.”

“Ron DeSantis rightly didn’t back down to the Experts(TM) during COVID and he likewise won’t let them keep him from securing our southern border,” said press secretary Bryan Griffin.

Former New Mexico Gov. Bill Richardson (D), a global crisis negotiator who served as U.S. permanent representative to the U.N. under Clinton, warned that military action in Mexico would both backfire and fail to solve the underlying issues.

“It shows the nativist shift of the Republican Party from internationalism to irresponsible diplomacy. It would be a disaster if there were any military action against Mexico — a foreign policy disaster for the United States,” he said. 

“Plus, it makes no sense to resolve the problem,” Richardson added.