On Monday, Attorney General Jeff Sessions threatened to pull funding from "sanctuary" jurisdictions unless those cities, counties, and states comply with a 1996 law that prohibits blocking communications between local police or sheriffs and federal immigration authorities about the immigration status of suspects in custody. Sessions also said the Justice Department will take steps to "claw back any funds awarded to a jurisdiction" that violates federal law, noting the DOJ will dole out more than $4.1 billion in such grants this year.
Sessions was acting under an executive order President Trump signed in January, but he didn't actually announce any new policy. Instead, The New York Times says, he was mostly restating aggressively grant eligibility rules former President Barack Obama issued last July. The law doesn't require local jurisdictions to honor "detainer" notices from federal immigration officials — requests to hold undocumented immigrants for up to 48 hours, without a warrant.
"Despite what Attorney General Sessions implied this afternoon, state and local governments and law enforcement have broad authority under the Constitution to not participate in federal immigration enforcement," New York Attorney General Eric Schneiderman said, nevertheless calling Trump's tactics "draconian." Tom Jawetz at the liberal Center for American Progress said Sessions' threat might not actually affect any U.S. city or county. "This is not really about enforcing the law, this is about driving policy through bullying and fear mongering," he said.
From Austin to Seattle, sanctuary jurisdictions said the Trump crackdown wouldn't affect their policies, most of which specifically state that law enforcement must comply with the law, U.S. Code 1373. There is no set definition of what a "sanctuary" jurisdiction is, and each city or county that refuses to comply with some aspect of Trump's immigration policy does so differently. CNN has a pretty good primer on what sanctuary cities actually do (and don't do):
The larger issue is how much the federal government can compel state and local law enforcement to carry out federal immigration policy. The 10th Amendment offers some protection to local jurisdictions, but the ACLU cautions that cities that do sign on to become part of Trump's "deportation force" face legal risks, too. "Because ICE does not seek a judicial determination of probable cause, these requests put local police in the position of holding people in jail without the legal authority to do so, which violates their constitutional rights," says the ACLU's Domenic Powell.