President Joe Biden is ceasing the execution of federal immigration laws, and the worst crisis in 20 years (by his own Department of Homeland Security secretary’s admission) is likely to reach an unprecedented level.

Let’s take a look at how we got here. On his first half-day in office, Biden’s DHS terminated enrollment in the Migrant Protection Protocols. Otherwise known as “Remain in Mexico,” this program provided that migrants who “illegally or without proper documentation” entered the United States from Mexico would be returned there while their claims for asylum were processed.