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Trump ordered his administration to broker deals with local authorities that empower and deputize local police in immigration matters in January; if widely enacted, former police they say this will make communities across the nation less safe, as individuals and whole neighborhoods stop reporting crime and cooperating with police for fear of deportations.

"If segments of the community are scared to call the police, those neighborhoods become an unsafe place for everyone who lives there,” explained Dr. Phillip Goff, co-founder and president of the Center for Policing Equity. “You don’t call the police, that becomes a breeding ground for illegal activity."

Cops in California told me Trump's "sanctuary city" executive order could hurt trust & public safety. #WhatNextUSA https://t.co/i5srgq0ukL — Jacob Soboroff (@jacobsoboroff) January 31, 2017

Police rely on family and friends outing criminals, the experts interviewed for this story stressed. "It’s hard enough to get someone to tell on their friends and family" without threatening them with deportation, Goff said.

Related: Trump vs. Reality: Tracking the President's Promises

Critics widely oppose deputizing local police in the immigration fight, citing racial profiling that has been reported in places like Maricopa County, Arizona, where Sheriff Joe Arpaio championed tough immigration enforcement, which courts say amounted to racial profiling, leaving taxpayers with a big bill to pay afterwards.

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But supporters say it's the only way to root out the estimated 11 million undocumented immigrants who are thought to be living in the United States.

The Center for Policing Equity researched the effect of local immigration enforcement on community policing efforts in Utah after a 2011 "show me your papers" law deputized police for immigration enforcement, digging into Salt Lake City’s Police Department’s police department records. The researchers found that that everyone — from minority and immigrant communities to legal, Caucasian citizens — trusted police less when local cops were tasked with seeking out and detaining undocumented immigrants.

A man is detained by Immigration and Customs Enforcement (ICE), agents early on Oct. 14, 2015 in Los Angeles, Calif. John Moore / Getty Images

“Across all races, religions, and creeds, people were less likely to call the police,” Goff said. “These kind of harsh policies toward immigration really do very little besides make us less safe.”

Chris Burbank, who was police chief in Salt Lake City at the time and now serves at the Center as the Director of Law Enforcement Engagement, said he recalled an undocumented woman whose child was kidnapped by an ex-husband.

“She refused to call the police about this, because she was afraid to be deported," said Burbank. "I heard about it through a back channel, and had to assure her we were not going to deport her for us to get involved," Burbank said. The child was recovered safely.

These fears are becoming reality in the Trump administration: A woman seeking a protective order against her abusive spouse was detained at a Texas courthouse after a local outlet reported that ICE was tipped off, possibly by her alleged abuser who was already in custody.

Goff said the research is "unequivocal" on this issue: "Cooperation with the law begins with trust in it, not fear in it. If you don’t understand that, you haven’t talked to anyone who has ever tried to enforce the law."

Trump already overstates American crime, as NBC News has previously reported, but he goes even farther when he talks about undocumented immigrants’ alleged propensity for crime (he says undocumented immigrants "present a significant threat" to public safety but, by the numbers, immigrants are less likely to commit crimes) and so-called sanctuary cities (he says they “breed crime,” the data just doesn’t back that up).

Trump supporters struggle with police as they attempt to cross the street during a counter-protest of the executive order by US President Donald Trump, banning immigrants from seven majority-Muslim countries at Los Angeles International Airport, California on February 4, 2017. KYLE GRILLOT / AFP - Getty Images

University of California Professor Tom Wong analyzed federal crime data and found that cities with "sanctuary" polices had significantly lower rates of all types of crime, including homicide, than comparable counties without policies that shielded undocumented immigrants from authorities.

Dennis Kenney, a former Florida police officer turned consultant and professor, said there’s an urban divide on the issue in America: Cities with diverse populations support keeping immigration enforcement out of municipal authorities hands, but rural sheriffs support doing it themselves — in part because they aren’t policing many immigrant neighborhoods whose trust they need to do their normal jobs.

Kenney, who has done international consulting on increasing community trust with local police, said that Trump’s harsh immigration rhetoric and policy is putting the nation on a path towards decreased trust in the authorities.

"The path we’re on — where black communities won’t talk to [police], Muslim communities won’t talk to them, Latino communities wont talk to them,” he said. The police “are going to stand on the street corner and talk to themselves."