Published August 16, 2017 Fox News

Attorney General Jeff Sessions heads to Miami Wednesday to praise the city for backing off its so-called sanctuary city policies as President Donald Trump has vowed to crack down on illegal immigration.

Sessions plans to highlight cities that cooperate with federal immigration officials during his visit to Miami. He is to be accompanied by Tom Homan, acting director of the U.S. Immigration and Customs Enforcement agency.

Miami-Dade County earlier this year reversed its sanctuary city policy, saying the county would honor requests to hold people for extra time so they can be arrested by immigration authorities. Local officials defended the decision, saying they wanted to keep receiving Justice Department grants for community policing.

Sessions is expected to “give remarks highlighting jurisdictions like Miami-Dade that have increased their cooperation and information sharing with federal immigration authorities and have demonstrated a fundamental commitment to the rule of law and lowering violent crime,” the Justice Department said in a release obtained by the Tampa Bay Times.

There isn’t a firm legal definition for sanctuary cities, and different cities may have dissimilar rules for how much they comply with federal immigration authorities.

Here’s a look at what sanctuary cities are and why they are so controversial.

What are sanctuary cities?

While the exact specifications can vary, sanctuary city policies overall limit just how much local law enforcement officials cooperate with federal immigration authorities.

San Francisco, for example, passed an ordinance in 1989 that prohibits city employees, funds or resources from assisting Immigration and Customs Enforcement (ICE) in enforcing federal immigration law unless it’s required by state or federal law.

It also passed an ordinance that limits when law enforcement officials can give ICE notice that an immigrant has been released from a local jail and prohibits law enforcement officials from cooperating with detainer requests from ICE.

Berkeley, near San Francisco, is reportedly the original sanctuary city. It passed a resolution in 1971 that protected sailors who wanted to resist the Vietnam War.

It’s difficult to nail down a concrete number of just how many cities are considered to be a sanctuary for immigrants – some cities have an ordinance or policy in place; others do not.

Aside from cities, at least five states – California, Oregon, Connecticut, Rhode Island and Vermont – have enacted laws that limit how much police can contribute to federal immigration agents, according to the New York Times.

The Immigrant Legal Resource Center argues that counties – not just cities – should establish sanctuary policies for undocumented immigrants.

How are they viewed?

The debate about sanctuary cities intensified in July 2015 when Katie Steinle, 32, was killed as she strolled along the San Francisco waterfront with her father. Steinle was fatally shot by a man with a criminal record who had slipped into the U.S. multiple times illegally.

Sessions addressed a roomful of federal prosecutors and law enforcement officials last month and criticized cities like Philadelphia that are "giving sanctuary" to criminals. He asked them to "reconsider the harm they are doing to their residents."

ILRC argues that local law enforcement jurisdictions do not have a “legal obligation to assist with civil immigration enforcement, which is the responsibility of the federal government.”

“A local decision to offer resources to federal immigration enforcement authorities is completely voluntary,” the legal organization said in a 2016 report.

ILRC called Trump’s threat to restrict federal funding of sanctuary cities “purely retaliatory in motivation.”

Many mayors of these cities have also bucked the threat and continued to affirm protection for immigrants.

"We are not going to sacrifice a half-million people who live amongst us, who are part of our communities, whose family members and loved ones happen to be people in many cases who are either permanent residents or citizens,” New York City Mayor Bill de Blasio, a Democrat, said in November.

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