Hundreds of thousands of undocumented migrants have been apprehended every year in recent years while trying to enter the US from Central American countries, including Honduras, Guatemala, and El Salvador. Mysteriously, however, the percentage of apprehended migrants from Mexico has dropped substantially. In 2004, US border patrol apprehended 1.1 million Mexicans, accounting for 9 out of 10 undocumented migrants that year. This number dropped to a low of 265 thousand in 2017 and then rose, to between 700 and 800 thousand in the early 2020s. So, what caused the number of undocumented Mexican migrants to plummet over time? Professor Jorge Dominguez recently set out to solve this mystery.