From the Background: "Since 2014, Mexico has experienced periodic surges in unauthorized migration from the 'Northern Triangle' of Central America (El Salvador, Guatemala, and Honduras). Mexico, like the United States, has struggled to deal with large numbers of families and unaccompanied minors, many of whom are seeking asylum. Under the threat of U.S. tariffs, Mexican President Andrés Manuel López Obrador accommodated Trump Administration policy changes that shifted some of the burden of interdicting migrants and hosting asylum seekers from the United States to Mexico. The Biden Administration has also sought Mexico's assistance in managing U.S.-bound migration flows."
CRS In Focus, IF10215
Congressional Research Service: https://crsreports.congress.gov/