San Francisco, Chicago and New York are among the major cities, as well as more than 200 small towns and counties and a dozen states, that over the past 40 years have adopted what is often known as sanctuary policies.

There is not a single definition of a sanctuary policy. But it often involves local authorities not asking about a resident’s immigration status, or not sharing that personal information with federal immigration authorities.

So when a San Francisco police officer pulls someone over for a traffic violation, the officer will not ask if the person is living in the country legally.

American presidents, from Ronald Reagan to Joe Biden, have chosen to leave sanctuary policies largely unchallenged since different places first adopted them in the 1970s. This changed in 2017, when President Donald Trump first tried to cut federal funding to sanctuary places, claiming that their policies “willfully violate Federal Law.” Legal challenges during his first term stopped him from actually withholding the money.

At the start of his second term, Trump signed two executive orders in January and April 2025 which again state that his administration will withhold federal money from areas with sanctuary policies.

“Working on papers to withhold all Federal Funding for any City or State that allows these Death Traps to exist!!!” Trump said, according to an April White House statement. This statement was immediately followed by his April executive order.

These two executive orders task the attorney general and secretary of homeland security with publishing a list of all sanctuary places and notifying local and state officials of “non-compliance, providing an opportunity to correct it.” Those that do not comply with federal law, according to the orders, may lose federal funding.

San Francisco and 14 other sanctuary cities, including New Haven, Connecticut, and Portland, Oregon, sued the Trump administration in February on the grounds that it was illegally trying to coerce cities to comply with its policies. A U.S. district court judge in California issued an injunction on April 24 preventing the administration —at least for the time being— from cutting funding from places with sanctuary policies.

However, as researchers who have studied sanctuary policies for over a decade, we know that Trump’s claim that sanctuary policies violate federal immigration law is not correct.

It’s true that the federal government has exclusive jurisdiction over immigration. Yet there is no federal requirement that state or local governments participate or cooperate in federal immigration enforcement, which would require an act of Congress.

In 1979, the Los Angeles Police Department was the first to announce a prohibition on local officials asking about a resident’s immigration status.

However, it was not until the 1980s that the sanctuary movement took off, when hundreds of thousands of Salvadorans, Guatemalans and Nicaraguans fled civil war and violence in their home countries and migrated to the U.S. This prompted a number of cities to declare solidarity with the faith-based sanctuary movement that offered refuge to Salvadoran, Guatemalan and Nicaraguan asylum seekers facing deportation.

In 1985, Berkeley and San Francisco pledged that city officials, including police officers, would not report Central Americans to immigration authorities as long as they were law abiding.

Berkeley also banned officials from using local money to work with federal immigration authorities.

“We are not asking anyone to do anything illegal,” Nancy Walker, a supervisor for San Francisco, said in 1985, according to The New York Times. “We have got to extend our hand to these people. If these people go home, they die. They are asking us to let them stay.”

Today, there are hundreds of sanctuary cities, towns, counties and states across the country that all have a variation of policies that limit their cooperation with federal immigration authorities.

Sometimes —but not always— places with sanctuary policies bar local law enforcement agencies from working with Immigration and Customs Enforcement, the country’s main immigration enforcement agency.

A large part of ICE’s work is identifying, arresting and deporting immigrants living in the U.S. illegally. In order to carry out this work, ICE issues what is known as “detainer requests” to local law enforcement authorities. A detainer request asks local law enforcement to hold a specific arrested person already being held by police until that person can be transferred to ICE, which can then take steps to deport them.

While places without sanctuary policies tend to comply with these requests, some sanctuary jurisdictions, like the state of California, only do so in the cases of particular violent criminal offenses.

Yet local officials in sanctuary places cannot legally block ICE from arresting local residents who are living in the country illegally, or from carrying out any other parts of its work.

Trump claimed in 2017 that sanctuary policies violated federal law, and he issued an executive order that tried to rescind federal grants that these jurisdictions received.

However, the 9th Circuit Court of Appeals ruled in a 2018 case involving San Francisco and Santa Clara County, California, that the president could not refuse to “disperse the federal grants in question without congressional authorization.”

Federal courts, meanwhile, split over whether Trump could freeze funding attached to a specific federal program called the Edward Byrne Memorial Assistance Grant Program, which provides about $250 million in annual funding to state and local law enforcement.

These cases were in the process of being appealed to the Supreme Court when the Department of Justice, under Biden, asked that they be dismissed.

Other Supreme Court rulings also suggest that the Trump administration’s claim that it can withhold federal funding from sanctuary places rests on shaky legal ground.

The Supreme Court ruled in 1992 and again in 1997 that the federal government could not coerce state or local governments to use their resources to enforce a federal regulatory program, or compel them to enact or administer a federal regulatory program.

To read the complete story, visit The Conversation.

Benjamin Gonzalez O'Brien is an associate professor of Political Science at San Diego State University. Loren Collingwood is an associate professor in the Department of Political Science at the University of New Mexico.

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