‘No country is more important to the United States than Mexico,’ President George H.W. Bush declared in a toast to President Carlos Salinas de Gortari during his state visit to Monterrey in November 1990. The adopted son of Houston, Texas, and erstwhile oilman understood better than most the deep cultural, economic, and security ties binding the two nations. Yet one need not hail from the Lone Star State to grasp the strategic significance of the US-Mexico partnership.

Bush’s words ring truer today than they did at that state luncheon 35 years ago. Back then, Mexico ranked as America’s third-largest trading partner, some 12 million Americans claimed Mexican heritage, and drug trafficking remained essentially a law-enforcement problem. Now, Mexico and the United States are inextricably intertwined, bound by not only shared history and culture, but also by integrated supply chains and energy. Some 40 million Americans are of Mexican heritage, representing more than half of the country’s Hispanic population. Mexico has become America’s top trading partner, eclipsing Canada as its biggest purchaser and China as its largest source of imports. The US-Mexico-Canada Agreement (USMCA), which superseded the North American Free Trade Agreement (NAFTA) in 2020, amplified these ties: bilateral trade reached $935.1 billion in 2024 and stands to exceed one trillion dollars this year. American markets and Mexican manufacturing are fused closer than ever, with US natural gas powering the bulk of Mexico’s electricity grid.

Deepening interdependence, however, has been accompanied by a grave security challenge. Drug cartels now threaten the United States and Mexico on a scale far greater than 35 years ago. The United States has designated the most powerful of them as Foreign Terrorist Organizations. Across swaths of Mexico, they rule by force and fear, imposing the macabre motto ‘plata o plomo’. You either get silver or lead.

Mexicans and Americans alike suffer from the cartels’ trade. The horrific violence in Mexico mirrors the scourge of drug overdoses in the United States. Last year, around 80,000 Americans died from overdoses, a welcome drop from the previous year’s 110,000 deaths, yet still the equivalent of the entire population of Napa, California, perishing in a single year.

Cartels are the epitome of a transnational criminal organisation. Deemed the most powerful organisations, the Sinaloa and CJNG cartels oversee global operations and outfits in all 50 states. Functioning as para-state entities, they engage in a host of illicit enterprises beyond narcotics, ranging from assassination, bribery, corruption, and extortion to arms dealing, fuel theft, and human and wildlife trafficking. Worse still, Chinese firms provide them with the precursor chemicals and equipment to manufacture fentanyl while Chinese money laundering organisations wash their proceeds, compounding the crisis with a great-power competition element.

Solving the intractable cartel problem is a trillion-dollar dilemma. The future of North American security, and with it the vast economic partnership between the United States and Mexico, depends on cooperation between two of the world’s most contrasting leaders: Presidents Donald Trump and Claudia Sheinbaum.

Can the consummate showman and right-wing populist team with the calculating scientist and technocratic left-wing populist? Mexico has served as Trump’s favourite foil. He catapulted into politics by promising mass deportations, the renegotiation of NAFTA, and a wall along the southern border. Even amid his tough talk, he routinely echoes past presidents when describing America’s sister republics as ‘our neighbours’ and lavishing praise on Sheinbaum for her bravery. Yet Trump has rarely engaged in diplomatic pageantry with Mexican presidents. As a candidate, Trump dramatically ventured to Mexico City in August 2016 for an unexpected meeting with then-President Enrique Peña Nieto. Once in office, he warmly hosted Sheinbaum’s predecessor Andrés Manuel López Obrador at the White House. Unlike his recent Republican predecessors, however, Trump has never visited Mexico as president, forgoing the chance to capitalise on the neighbourly symbolism.

Republican presidents once revelled in the opportunity. Two weeks before his inauguration, Ronald Reagan greeted Mexican president José López Portillo on the Cordova Bridge between Ciudad Juárez and El Paso. In October 1982, Reagan held another cross-border visit with president-elect Miguel de la Madrid in Tijuana, Mexico, and Coronado, California. Of course, Reagan’s successor, George H.W. Bush, likewise thought of Mexico as a neighbour and friend, cheering at his arrival ceremony in Monterrey: ‘viva Mexico!’

Like his father, President George W. Bush, the former governor of Texas, understood the vital nature of the partnership with Mexico. For his first trip abroad, he travelled to San Cristóbal, Mexico, to meet President Vicente Fox at his ranch. With Fox’s successor, Felipe Calderón, Bush fashioned the bipartisan security cooperation framework that drove US-Mexican efforts to combat narcotics trafficking for thirteen years. The Mérida Initiative supplied Mexico with American intelligence, training, and equipment in a joint campaign to dismantle cartels and reform its judicial system.

The Mérida Initiative collapsed during Trump’s first term. President López Obrador made good on his campaign slogan ‘Abrazos, no balazos’ – hugs, not bullets – and steadily defanged it. Meanwhile, he helped Trump with his signature policies of border enforcement and replacing NAFTA. At their July 2020 meeting in Washington, Trump proclaimed of Mexico: ‘We’re cherished friends, partners, and neighbours’. López Obrador responded in kind, thanking Trump for upholding Mexican sovereignty by eschewing the Monroe Doctrine. But his actions spoke louder than his words.

Three months later, López Obrador rendered the Mérida Initiative defunct. In October 2020, the Drug Enforcement Agency (DEA) arrested Mexican General Salvador Cienfuegos Zepeda for drug-trafficking. Furious, López Obrador demanded his release, admonished Washington, and restricted security cooperation. At this juncture, López Obrador had already dissolved the Federal Police, supplanting them with the National Guard. He eventually signed a law circumscribing the role of foreign agents and closed the DEA’s Sensitive Investigative Unit in Mexico City that had operated for 25 years.

Under President Joe Biden, the Mérida Initiative formally ended. Biden and López Obrador settled on a new agreement, the Bicentennial Framework for Security, Public Health, and Safe Communities, which prioritised social development over law enforcement. The results were more death, drugs, and despair. In López Obrador’s final year, reports emerged that the United States had probed his alleged cartel connections. He left office in October 2024, with over 200,000 homicides recorded during his six-year term.

Given the recent political turbulence and policy complications, the current state of US-Mexico security cooperation can seem perplexing. On the one hand, rhetoric coming out of Washington and Mexico City raises the prospect of a trade war that could wreck Mexico’s economy and the deployment of US armed forces into Mexican cities against Sheinbaum’s wishes. On the other hand, Trump and Sheinbaum speak regularly by telephone, and the anti-cartel efforts between Mexico and the United States have grown closer and more intense.

Trump wields American economic and military power as a blunt reminder to Mexico of its security obligations. Trump openly floats the possibility of direct US strikes on cartels and brandishes punishing tariffs. The pattern is predictable and effective. In February, he first proposed a 25 per cent tariff on Mexican imports over the fentanyl epidemic, which never materialised after Sheinbaum met Trump’s demands for enhanced border security and drug enforcement. Not entirely satisfied, Trump sought to levy a 30 per cent tariff in July, but his discussions with Sheinbaum delayed it. He has also repeatedly offered to send US troops to Mexico, only for Sheinbaum to reject it outright. Each time Trump escalates, Sheinbaum negotiates and advances Mexico’s anti-narcotic campaign.

To be sure, Mexican sovereignty sets clear limits on US-Mexican security cooperation. The historical memory of the Mexican-American War, in which the United States acquired half of Mexico’s territory, remains vivid in Mexico City. No American president, however, has authorised a unilateral military intervention on Mexican soil since the Punitive Expedition against Pancho Villa over a century ago.

Still, Trump’s provocative proposals place Sheinbaum in an awkward but advantageous position. At home, the popular Sheinbaum defends Mexican sovereignty against the superpower to the north. Abroad, she quietly accommodates Trump’s calls for stronger cooperation, much to his liking. She has compelling political and economic incentives for doing so.

Sheinbaum’s flagship Plan México, an ambitious agenda for economic development, and the political future of the ruling Morena party, hinges on her ability to reduce crime. Nationwide protests in November over corruption and crime, organised by the ‘Gen Z’ movement and inspired by the murder of an anti-cartel mayor, coupled with a third quarter slump in gross domestic product, reflect a worrisome trend. The combination of rampant violence and a recession could undermine her presidency. On the cartel problem, then, Mexican and American interests align.

Sheinbaum’s actions have complemented Trump’s bid to degrade cartels under his ‘Americas First’ strategy, which marks a return to hemispheric defence. The proof lies in the arrests and the bloodshed.

Upon taking office, Sheinbaum dispensed with ‘hugs, not bullets’. She appointed Omar García Harfuch, the former Mexico City police chief who survived a cartel hit in 2020, as the Secretary of Security and Citizen Protection. García Harfuch has tackled organised crime with gusto, impressing his American counterparts. As security minister, he has created the National Operation Unit, an investigative body with a special forces component, and placed a trusted, capable team in key security roles throughout the government, all of which reoriented the Mexican security state toward maximum confrontation with the cartels.

Together, the United States and Mexico wage a 21st-century battle against cartels. In September, Secretary of State and acting National Security Advisor Marco Rubio met with Sheinbaum to reaffirm the security partnership. The arrangement respects Mexico’s ‘cooperation without subordination’ stance and expands joint operations. The US-Mexico Security Implementation Group, established thereafter, streamlines high-level coordination on security programmes, including on the illicit flow of arms into Mexico, a longstanding priority for Mexican authorities. Subsequent cooperative efforts have included an increased crackdown on money laundering, as well as capturing and extraditing wanted international fentanyl brokers, like Zhi Dong Zhang, known as ‘Brother Wang’.

High-value extraditions, mostly handled by García Harfuch, have become a feature of US-Mexico security cooperation. Mexico has turned over more than fifty cartel members since Trump’s second inauguration. The most notable example came earlier this year. Mexico extradited drug lord Rafael Caro Quintero, who killed DEA agent Enrique ‘Kiki’ Camarena in 1985, ending Washington’s four-decade quest to imprison him in America.

Even before the high-level implementation group’s formation, the United States and Mexico had accelerated joint operations for border enforcement, targeted arrests, arms and drug interdictions, and clandestine lab raids. In February, thousands of Mexican National Guard troops surged to the US-Mexico border. At the request of Mexico, intelligence sharing also expanded significantly. On the American side, US Northern Command oversees surveillance. Inside Mexico, however, the Central Intelligence Agency (CIA) has undertaken a greater role in intelligence gathering, conducting drone surveillance and providing targeting data for raids in close coordination with Mexican counterparts.

For many years, the CIA has conducted operations in Mexico to capture high-ranking cartel members. At Mexico’s invitation, the CIA works alongside special American-trained and vetted Mexican army and navy units. US Ambassador Ronald Johnson, a retired Army Green Beret and former CIA officer, even shares his floor in the embassy with CIA analysts. Inside the United States, the priority of anti-narcotic operations has led the Agency to stand up the Americas and Counternarcotics Mission Center, from which it doggedly seeks to eradicate cartels at Trump’s command.

The drug war has taught many sobering lessons, not the least of which is that we must temper expectations. The US-Mexico security relationship has sticking points. Endemic corruption in Mexico has plagued anti-narcotic initiatives for decades, permitting cartels to infiltrate every institution. Trump consistently presses Sheinbaum to pursue vigorous anti-corruption measures, especially against members of Morena. Last month, the US State Department revoked the visas of an estimated 50 officials, most from Morena, for suspected links to cartels. The escalation signalled the intent of the Trump administration. Whether Sheinbaum risks destabilising her presidency and diminishing her party to secure her country remains to be seen. Washington looks on with anticipation.

Thirty-five years ago in Monterrey, Bush expressed a sentiment about America’s interdependence with Mexico that only sounds truer with time. The neighbourly relationship that he celebrated has never been more consequential or perilous. Back then, cartels were an urgent law-enforcement problem, not one of the gravest national security challenges to face North America. Today, the United States and Mexico have entered a new age of security cooperation, one that carries vastly higher financial stakes and a much steeper human toll. Hard decisions and difficult compromises now await leaders on both sides of the Rio Grande.