The modern idea traces to the 1980s sanctuary movement, when churches sheltered Central American refugees denied asylum by the US. Cities began passing their own policies, including San Francisco's City of Refuge ordinance in 1989. California passed a statewide law, SB 54, in 2017.
Sanctuary policies rest on two points. Local police are not required to enforce federal civil immigration law, because the Tenth Amendment bars the federal government from commandeering state and local officials. Supporters also argue that immigrants will not report crimes or cooperate with police if any contact could lead to deportation.
The federal government has repeatedly tried to punish these jurisdictions. In 2025, the Trump administration moved to cut federal funding to sanctuary cities and counties. That year, a federal judge in San Francisco blocked those cuts for dozens of jurisdictions, ruling that the conditions were likely unconstitutional.