U.S. Examined Allegations of Cartel Ties to Allies of Mexico’s President

American law enforcement officials spent years looking into allegations that allies of Mexico’s president, Andrés Manuel López Obrador, met with and took millions of dollars from drug cartels after he took office, according to U.S. records and three people familiar with the matter.

The inquiry, which has not been previously reported, uncovered information pointing to potential links between powerful cartel operatives and Mexican advisers and officials close to the president while he governed the country.

But the United States never opened a formal investigation into Mr. López Obrador, and the officials involved ultimately shelved the inquiry. They concluded that the U.S. government had little appetite to pursue allegations against the leader of one of America’s top allies, said the three people familiar with the case, who were not authorized to speak publicly.

Mr. López Obrador called the allegations “completely false,” responding to questions from The New York Times on Thursday. He said the news of the inquiry would not “in any way” affect Mexico’s relationship with the United States, but said he expected a response from the U.S. government.

“Does this diminish the trust the Mexican government has in the United States?” Mr. López Obrador said at a regular news conference, adding, “Time will tell.”

Drug cartels have long infiltrated the Mexican state, from the lowest levels to the upper reaches of government. They pay off the police, manipulate mayors, co-opt senior officials and dominate broad swaths of the country.

But while the recent efforts by the U.S. officials identified possible ties between the cartels and Mr. López Obrador’s associates, they did not find any direct connections between the president himself and criminal organizations.

American officials declined to comment.

Much of the information collected by U.S. officials came from informants whose accounts can be difficult to corroborate and sometimes end up being incorrect. The investigators obtained the information while looking into the activities of drug cartels, and it was not clear how much of what the informants told them was independently confirmed.

For example, records show that the investigators were told by an informant that one of Mr. López Obrador’s closest confidants met with Ismael Zambada García, a top leader of the Sinaloa drug cartel, before his victory in the 2018 presidential election.

A different source told them that after the president was elected, a founder of the notoriously violent Zetas cartel paid $4 million to two of Mr. López Obrador’s allies in the hope of being released from prison.

Investigators obtained information from a third source suggesting that drug cartels were in possession of videos of the president’s sons picking up drug money, records show.

Mr. López Obrador denied all the allegations made by the informants.

The U.S. law enforcement officers also independently tracked payments from people they believed to be cartel operatives to intermediaries for Mr. López Obrador, two of the people familiar with the inquiry said.

At least one of those payments, they said, was made around the same time that Mr. López Obrador traveled to the state of Sinaloa in 2020 and met the mother of the drug lord Joaquín Guzmán Loera, who is better known as El Chapo and is now serving a life sentence in an American federal prison.

More than a decade ago, a separate investigation led by the Drug Enforcement Administration unearthed allegations that traffickers had donated millions to Mr. López Obrador’s unsuccessful presidential campaign in 2006. This inquiry, which was detailed by three media outlets last month, was closed without charges being brought.

For the United States, pursuing criminal charges against top foreign officials is a rare and complicated undertaking. Building a legal case against Mr. López Obrador would be particularly challenging. The last time the United States filed criminal charges against a top Mexican official, it ultimately dropped them after his arrest caused a diplomatic rift with Mexico.

The Biden administration has an enormous stake in managing its relationship with Mr. López Obrador, who is seen as indispensable to containing a surge in migration that has become one of the most contentious issues in American politics. It is a major concern for voters in the lead up to the presidential election this fall.

Mexico is also a top American trading partner and the single most important collaborator in U.S. efforts to slow illicit drugs like fentanyl from crossing the southern border.

U.S. law enforcement agencies have jurisdiction to investigate and bring charges against officials of other countries if they can show a connection to narcotics moving across the border into the United States.

While it is uncommon for American agents to pursue top foreign officials, it is not unprecedented: The drug trial of Juan Orlando Hernández, the former president of Honduras, began this week in Federal District Court in Manhattan.

Federal prosecutors in New York also secured a corruption conviction last year against Genaro García Luna, Mexico’s former public security secretary, persuading a jury that he had taken millions of dollars in bribes from violent cartels he was meant to be pursuing.

While efforts to scrutinize Mr. López Obrador’s allies are no longer active, the revelation that U.S. law enforcement officials were quietly examining corruption allegations against them could itself be damaging.

Last month’s media reports, including one by ProPublica, about a U.S. inquiry into 2006 campaign donations — for an election he did not win — ignited a firestorm in Mexico.

Mr. López Obrador publicly denounced the stories, implying they were aimed at influencing the country’s presidential election in June, in which his protégé, the former Mexico City mayor Claudia Sheinbaum, is leading the race to replace him. He suggested the reports could complicate talks on migration and fentanyl with the U.S. government, and said he considered not receiving President Biden’s homeland security adviser for a planned meeting in the Mexican capital.

“How are we going to be sitting at the table talking about the fight against drugs if they, or one of their institutions, is leaking information and harming me?” Mr. López Obrador said at a regular news conference days after the stories published.

After President Biden called Mr. López Obrador, calming tensions, the Mexican foreign minister said that the U.S. homeland security adviser told Mexico “that this is a closed issue for them.”

The Biden administration has handled Mr. López Obrador with great care, avoiding public criticism in favor of repeatedly dispatching top officials to Mexico City to meet with him and press for sustained migration enforcement in private.

The decision to let the recent inquiry go dormant, the people familiar with it said, was caused in large part by the breakdown of a separate, highly contentious corruption case. In the closing months of the Trump administration in 2020, U.S. officials brought charges against Gen. Salvador Cienfuegos Zepeda, who served as Mexico’s defense secretary from 2012 to 2018.

In a federal indictment, unsealed in New York after a multiyear investigation named “Operation Padrino,” prosecutors accused General Cienfuegos of using the powers of his office to help a violent criminal group called the H-2 cartel conduct its drug trafficking operations.

His arrest at the Los Angeles airport provoked a furor within the Mexican government, particularly among the leaders of the country’s armed forces, which have assumed greater responsibilities and power under Mr. López Obrador.

The president said the charges were “fabricated” and his administration released more than 700 pages of communications intercepted by U.S. agents that purported to show criminal activity but were cast as inconclusive.

The Drug Enforcement Administration, which already had a checkered history as protagonists in a drug war seen as bloody and futile, suffered a tremendous blow to its relationship with the Mexican government.

Just weeks after the arrest took place, the U.S. Justice Department, under heavy pressure from Mr. López Obrador, reversed itself and dismissed the indictment, sending General Cienfuegos back to Mexico.

The episode not only damaged longtime security arrangements between the two countries, but also left a deep impression on law enforcement officers north of the border, many of whom saw the failed case as a cautionary tale about undertaking similar efforts against other high-ranking Mexican officials.

Emiliano Rodríguez Mega contributed reporting.