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...