Andrés Manuel López Obrador’s personalistic style of governing is a form of democratic backsliding. His leadership is affecting U.S.-Mexican relations in a way that could turn back the clock on three decades of economic integration, revive the previous mistrust between the two countries, and halt collaboration on issues of binational concern. The Biden administration does not seem to fully understand the dangers that loom ahead as Mexico becomes a more insecure, more militarized, and less democratic country.