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Q & A: What is a sanctuary city?

President Trump’s pledge to withhold federal money from so-called sanctuary cities has reignited controversy over the role that local law enforcement and officials have in immigration regulation.

The Globe asked Boston College law professor Kari Hong, who specializes in immigration, to answer some basic questions on how sanctuary cities work in politics and practice. Her responses have been edited for clarity and length.

What is a sanctuary city, and how did that term originate?

The term implies that cities are providing protection for undocumented immigrants or defiance of the law. It is not that.

The sanctuary city term likely came from activists who believe it offered more protection than it actually offered. The activists believe that immigration laws will no longer apply or be enforced in a sanctuary city. That is not true. It’s just that the federal government has to do the enforcement and not the local police. And the federal government is always allowed to do that enforcement, even in sanctuary cities. They have to bring their own agents, get their own information, and put the people in their own detention facilities.

So if Mayor Martin J. Walsh, as promised, opens up City Hall to undocumented immigrants for shelter, can the city prevent federal authorities from getting inside the building?


No. And no one is asking to do that. As an example, some college campuses offer sanctuary to their undocumented students. The federal government can say, “give me the names of your noncitizens,” and the campuses can refuse. But if the federal government returns with a warrant, the colleges will have to provide the information.

So is sanctuary city just a political term?

Yes, unfortunately. It is not an official designation. Its use started under President George W. Bush’s Secure Communities Program, which asks cities and states to work with the federal government on deportation enforcement by running background checks on those they arrest and then detain until Immigration and Customs Enforcement authorities determine if they are deportable. The federal government’s effort was renamed the Priority Enforcement Program under President Obama.


The reason why cities began to decline helping the federal government is because the federal authorities told them they were going to get all the bad guys — the drug dealers, rapists, and murderers — out of cities and towns. But what was happening was that about 40 percent had no criminal record and 16 percent had minor crimes, such as undocumented immigrants who were driving without a driver’s license on the way to drop their kid to school. The states and cities were also stuck detaining immigrants for years and were not being reimbursed by the federal government. The effort ended up costing millions.

Meghan E. Irons can be reached at Follow her on Twitter @meghanirons.