NEW YORK — Ignoring fresh threats from the White House, city leaders across the U.S. are vowing to intensify their fight against President Donald Trump’s promised crackdown on so-called “sanctuary cities” despite the financial risks.

“We are going to become this administration’s worst nightmare,” New York City Council Speaker Melissa Mark-Viverito said Monday during a gathering of municipal officials from urban centers such as San Francisco, Seattle, Denver, Chicago and Philadelphia.

As is the case in several sanctuary cities, they promised to continue blocking cooperation between city police departments and federal immigration authorities. They also vowed to prevent federal agents from accessing their schools and school records, and they openly contemplated employing cities’ rarely-used oversight and subpoena powers to investigate federal immigration practices.

The defiance that filled the New York City conference clashed with pointed warnings from the White House’s West Wing, where Attorney General Jeff Sessions issued a dire warning to urban leaders who embrace policies that help protect immigrants in the country illegally from deportation.

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Such policies, Sessions said, “endanger the lives of every American” and violate federal law. He said the Trump White House could withhold or “claw back” funding from any city that “willfully violates” immigration law.

Sessions said the Justice Department would require cities seeking some of the $4.1 billion available in grant money to verify they are in compliance with a section of federal law that allows information sharing with immigration officials.

“I strongly urge our nation’s states and cities and counties to consider carefully the harm they are doing to their citizens by refusing to enforce our immigration laws, and to rethink these policies,” he charged.

The debate highlighted the nation’s increasingly polarized view of immigration.

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Trump won the presidency by appealing to white working-class voters in a campaign that regularly highlighted violent crimes committed by immigrants in the country illegally. Sessions drew from the same playbook at the White House podium on Monday, citing two recent murders committed by immigrants released by local authorities even though they were wanted by federal agents.

City leaders insisted such examples are the exception, not the rule. Philadelphia City Council member Helen Gym said immigrants in the country illegally are part of the “fabric of America.”

“It’s not like immigrants are dangerous. They’re actually the ones in the most danger,” Gym said, citing labor and housing practices that discriminate against immigrants.

Indeed, city officials on Monday shared stories of immigrants in their communities seized by federal immigration agents at their children’s schools and at courthouses as they appeared as victims of other crimes. Gym said some landlords have used Trump’s hardline immigration rhetoric to expel immigrant tenants.

There are an estimated 11 million immigrants living in the country illegally. There is no evidence that crime rates among immigrants are higher than native-born Americans.

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Trump has made illegal immigration a priority.

He issued an executive order in January that directs the Secretary of Homeland Security to publish a weekly list of “criminal actions committed by aliens.” The administration last week reported more than 200 cases of immigrants recently released from local jails before federal agents could intervene.

Lourdes Rosado, who leads the New York attorney general’s civil rights bureau, insists that municipalities have legal standing to resist what she described as immigration overreach by the new White House.

“Sessions makes it sound as if we’re breaking the law. But the point is, it’s voluntary whether or not to cooperate,” Rosado said, acknowledging that states and cities may have to resolve the issue in court. “Will they come after you? Maybe.”