In late April, the White House issued yet another executive order threatening to withhold federal funds from all “sanctuary” jurisdictions, calling their lack of cooperation with federal immigration authorities “a lawless insurrection against the supremacy of Federal law.”

The executive order directs the Department of Justice, attorney general and Secretary of Homeland Security to provide a list of all sanctuary cities in order to suspend or terminate federal funding, including grants and contracts. Earlier this year, Trump’s Department of Justice directed federal prosecutors to investigate and criminally charge public officials who do not comply with federal immigration enforcement.

Days after the executive order was released, the Department of Justice filed a lawsuit targeting the sanctuary jurisdictions of Colorado and the city and county of Denver, as well as government officials including Colorado Gov. Jared Polis, Attorney General Phil Weiser, the state legislature, Denver Mayor Mike Johnston and Denver Sheriff Elias Diggins. Chicago and Illinois were targeted in a similar lawsuit in February, as was Rochester, New York, in late April.

While experts say legal precedent and the law remain in favor of sanctuary policies, we’ve already seen Trump follow through on his threats to revoke federal funding from cities, states and universities that have challenged him — which could mean that litigant responders who were quick to fight in 2016 might not be so quick to respond this time.

What is a sanctuary city?

A sanctuary city is defined by its commitment to limit or refuse to share information with federal immigration officers, like ICE and CBP, regarding its constituents or citizens.

“When we see localities cooperating with federal immigration enforcement, that’s often a way that people end up in the immigration system,” explains Jennifer Lee, associate professor of law at Temple University’s Beasley School of Law. “So once you de-link those two things, it helps to protect immigrants from ending up in that system.”

The term “sanctuary” is a broad term with little legal or universal determination, meaning it can cover a broad array of policies implemented by states, cities, jurisdictions, buildings and other entities.

Churches, for example, can identify as a sanctuary building, meaning that they do not allow any ICE officer inside the property. Schools and school districts can also offer “sanctuary policies,” meaning they do not work with or provide information for ICE or CBP regarding their students.

Since 2021, Philadelphia has implemented a sanctuary school policy that aims to protect students from federal immigration authorities regardless of immigration status. That means that the school district won’t comply with an administrative warrant, though it would likely be required to comply with a judicial warrant issued under federal law.

How many sanctuary cities are there?

There are at least 12 sanctuary states across the U.S., including California, Massachusetts, Illinois, New Mexico and Washington, and at least 633 cities and counties with some type of sanctuary policy.

With definitions varying, it can be tricky to nail down exact numbers. Some counties or cities may have identified their jurisdiction as a sanctuary for immigrants, but not have any actual sanctuary policies on the books — and vice versa.

How do sanctuary cities actually protect immigrants?

Preventing local authorities from assisting in federal immigration enforcement reduces the amount of resources that the federal government has to conduct its deportation and other enforcement campaigns, Lee says. “There’s only so much funding, there are only so many officers,” she says. “They don’t have the infrastructure, they don’t have the wherewithal.”

Sanctuary cities generally offer much less protection than is often assumed, but they do still offer meaningful protection for undocumented people. According to the American Immigration Council, sanctuary policies typically fall into several different categories, including policies that restricting state and local police’s ability to arrest or detain individuals over civil immigration violations, bans on immigration detention centers, bans on 287(g) agreements (which allow ICE to deputize local law enforcement officers to enforce federal immigration law) and more.

ICE and CBP can still arrest undocumented immigrants in sanctuary cities, but per city ordinances, local law enforcement may not be allowed to detain undocumented immigrants for federal immigration violations or share information on undocumented immigrants with the federal government.

However, sanctuary entities cannot keep ICE or CBP from detaining someone, and they may be required to comply with judicial warrants.

Federal agencies are required to provide such judicial warrants when entering private property. However, as we’ve seen over the last few months, many of these arrests are not happening in private spaces: They’re taking place outside of churches, outside of their children’s schools, or on people’s way to civil court.

Usually, ICE agents have an administrative warrant, which is signed by a supervisor within the agency rather than a judge, Lee says.

“In theory, if somebody went to a school and had a judicially approved warrant, the school would probably have to let them in, but that’s just not something we hear about,” she explains. “What we hear about, rather, is that they show up at places with administrative warrants. And so if you have that protection in place, it can protect people.”

How are sanctuary cities responding to Trump’s executive order?

Following Trump’s previous order to cut federal funding to sanctuary cities, a group of 16 cities and counties led by San Francisco filed a joint federal lawsuit in February. Late last month, a judge blocked the Trump administration from withholding these funds, leading to the newly issued executive order.

Many local and state government officials have reiterated their commitment to their sanctuary policies in the face of these renewed threats. The City of Rochester, New York, which was sued in late April, has promised to fight the Department of Justice’s lawsuit, as has Denver’s mayor in a similar lawsuit.

But as universities lose funding and large law firms are sued by Trump, sanctuary cities are already seeing the consequences of their commitment to their sanctuary status. With billions of dollars of local and state budgets on the line, experts say some cities might roll over out of fear.

Lee says that’s likely a larger threat to sanctuary cities than the order itself. “The threat feels so overwhelming that the easiest kind of thing to do is just to kind of preemptively obey whatever’s coming at you, versus fight it,” she says.

Are sanctuary cities legal?

Yes, sanctuary cities are legal.

Lee explains that their legality is clearly stated under the 10th Amendment, which states that the federal government “may neither issue directives requiring the States to address particular problems, nor command the States’ officers, or those of their political subdivisions, to administer or enforce a federal regulatory program” — such as immigration enforcement.

“There’s a line of Supreme Court cases that basically say that the 10th Amendment protects against federal government commandeering, and so it’s very clear what sanctuary cities are doing,” Lee explains. “They’re saying, ‘We’re not going to do the federal government’s job. We’re going to delink our databases, or we’re not going to collaborate in these specific ways,’ and that’s absolutely permissible under the 10th Amendment.”

During Trump’s first term, his then-Attorney General Jeff Sessions sued California over its sanctuary law. A federal appeals panel upheld the law, ruling that “California has the right … to refrain from assisting with federal efforts.”

How does aggressive immigration enforcement impact public safety in cities?

Research shows that in immigrant communities, people may fear reporting crimes, testifying in court or coming forward as witnesses out of fear of being targeted for detention or deportation. “A number of law enforcement agencies across the country find sanctuary-type policies to be really important for that reason,” Lee says. “They know that that’s the way to effectively do their jobs and maintain public safety.”

While Trump and anti-immigrant politicians have often linked immigration and sanctuary policies to higher crime rates, experts say that’s not the case.

“This notion that immigrants are somehow a threat to public safety is completely untrue,” says Shayna Kessler, director of the Advancing Universal Representation Initiative at the Vera Institute of Justice. “A higher proportion of immigrants just does not equate to any associated higher occurrence of crime, and the evidence is really clear.”

According to a report by the Center for American Progress, there are, on average, 35.5 fewer crimes committed per 10,000 people in sanctuary counties compared to non-sanctuary counties.

Another study co-authored by Santiago Pérez, associate professor of economics at UC Davis, finds that immigrant men have had a lower incarceration rate than U.S.-born men for the last 150 years of American history and continue to do so. Immigrant men are also 50-60% less likely to be incarcerated than U.S.-born men.

“When we talk about ramping up integration enforcement, what we’re really doing is making communities less safe and less stable, by separating families, by upending businesses, and by destabilizing the very people who make our communities strong and stable,” Kessler says.

How were sanctuary cities created?

While sanctuary cities have been highly politicized as providing refuge for immigrants, that’s not how they began. It was actually tied to California’s anti-war movement during the Vietnam War.

One Sunday over 50 years ago, a member of University Lutheran’s Chapel in Berkeley, California, burned his draft card in the church parking lot. The FBI, stationed across the street, witnessed the event and arrested the man after he left the church service.

In the months that followed, about 1,000 active military crew members formed an organization called Stop Our Ship, after being given military orders to ship off from Alameda County and signed an anti-war petition. For two to three days after, the City of Berkeley joined the ULC church and anti-war protesters in defending the crew members by engaging in a standoff against federal and state law enforcement. The city council later adopted Resolution 44,784, calling itself a City of Refuge — the first in the nation — for any crew members and designating the ULC as a city-approved sanctuary.

Almost a decade later, five San Franciscan churches signed a declaration that would launch the sanctuary city movement nationally. During the 1980s, U.S. immigration policies denied Central Americans refuge. Churches, synagogues and faith-based organizations declared a form of “sacred resistance” where they advocated for this community by defying federal authorities and providing shelter, aid and support to Central American refugees. On 1982, five San Francisco Bay Area churches joined Southside Presbyterian Church in declaring their churches to be sanctuaries for Central Americans.

“We are writing to inform you that the Southside Presbyterian Church will publicly violate the Immigration and Nationality Act Section 274(a). We have declared our church as a ‘sanctuary’ for undocumented refugees from Central America,” they wrote. “The current administration of U.S. law prohibits us from sheltering these refugees from Central America. Therefore, we believe the administration of the law to be immoral as well as illegal.”

This post was originally published on Next City.