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From New York to Los Angeles, leaders in the nation's largest sanctuary cities are denouncing President Trump's "crackdown" on communities that shield undocumented immigrants from deportation.

"We will not be intimidated by the threat to federal funding," Boston Mayor Marty Walsh said at a press conference Wednesday flanked by immigrant city workers.

"I want everyone to just get a picture of those behind me today," he said. "This is America who’s behind me: the many immigrants who work for the city of Boston and the many first generation Americans who work for the city of Boston."

Walsh spoke out after Trump signed an executive order earlier Wednesday eliminating most federal funding for cities with sanctuary policies in place.

Trump’s executive order, titled "Enhancing Public Safety in the Interior of the United States," would make communities that do not fully comply with federal immigration enforcement agencies, ineligible "to receive Federal grants, except as deemed necessary for law enforcement purposed by the Attorney General or the Secretary [of Homeland Security]."

Related: Trump Signs Executive Orders Targeting Illegal Immigration

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New York Attorney General Eric T. Schneiderman, a Democrat who sued the president for fraud in the case involving Trump University, said that he would fight the executive order.

"The President lacks the constitutional authority to cut off funding to states and cities simply because they have lawfully acted to protect immigrant families," Schneiderman said in a statement. "Local governments seeking to protect their immigrant communities from federal overreach have every right to do so."

New York City Mayor Bill de Blasio, also a Democrat, said Trump's executive order would not change policing in his city.

"The stroke of a pen in Washington D.C. does not change the people of New York City or our values," de Blasio said. "It does not change how this city government protects its people and it will not change how we enforce the law in New York City or how we do business on behalf of the people all 8.5 million New Yorkers."

In California, Attorney General Xavier Becerra said Trump's executive orders does not Trump existing law. Among other things, his state has passed laws limiting local jails from holding low-level offenders just so they can be deported, among other protections.

"These are rights and protections which have survived numerous legal challenges over time. And they are grounded on our federal and state constitutions not on an executive pronouncement," Becerra said.

I can't say it any more clearly: DC will remain a #SanctuaryCity to keep all of our residents safe https://t.co/QSXehZ8VUl #DCvalues pic.twitter.com/b2tCJMRBc1 — MurielBowser (@MurielBowser) January 26, 2017

Los Angeles Mayor Eric Garcetti said they cooperate with immigration officials, but said the LAPD will not enforce federal immigration laws. "That’s an official LAPD policy that has been enforced for nearly 40 years," he said.

"That is for everyone’s good, because trust between police and the people they serve is absolutely essential to effective law enforcement," he said.

"The executive order does not change the mission of the Los Angeles County Sheriff's Department," chimed-in Sheriff Jim McDonnell.

"Our department policy clearly states that our deputies do not ask for one’s immigration status," he said in a statement. "Immigration enforcement remains a federal responsibility."

There was more defiance from the mayors of Chicago, Washington, San Francisco and Seattle.

"We will not be intimidated by the authoritarian message coming from this administration," Seattle Mayor Ed Murray said.

Seattle Police Chief Kathleen O’Toole said that local law enforcement must be able to protect and also communicate with undocumented immigrants. "Police leaders across the country are aligned on this issue," she said.

But Trump's move also drew praise from some corners.

"I fully support the president in withholding federal funding from cities who engage in sanctuary city polices," Louisiana Attorney General Jeff Landry said. "Sanctuary city policies are dangerous to citizens who are lawfully in this country."

The National Border Patrol Council, a union that represents Border Patrol employees, praised Trump's executive action as well as his proposed wall on the U.S. and Mexican border. "This has been a long day coming," the union said in a statement.