The term “sanctuary city” has become a political lightning rod. Two years ago, Texas lawmakers tried and failed to pass a bill to restrict cities and institutions from being “sanctuaries” for undocumented immigrants.

The term "sanctuary city" has become a political lightning rod. Two years ago, Texas lawmakers tried and failed to pass a bill to restrict cities and institutions from being "sanctuaries" for undocumented immigrants.

LISTEN: The KERA radio story.

Gov. Greg Abbott and President-elect Donald Trump have joined that call, and a new bill is on the table in Austin. Senate Bill 4 would ban "sanctuary cities." Law enforcement officials held a press conference Wednesday to oppose the proposed legislation.

Captain Shelley Knight is with the Dallas County Sheriff's Department.

"Our job as law enforcement is to protect our communities," Knight said. "If you pass Senate Bill 4, what that will do is cause us to be federal immigration officers. And we will lose the trust of the communities that we have."

Meanwhile, last December, students at two Denton universities held rallies to have their schools declared "sanctuary campuses." But defining what a sanctuary is... isn't so easy.

It's a buzz phrase guaranteed to get cheers on the campaign trail.

Abbott has declared that Texas will pass a law banning sanctuary cities. And during his campaign, Trump said the government will block funding from sanctuary cities.

Abbott and Trump seem pretty sure of the definition. But things can get kind of tricky, said Elissa Steglich, an immigration law professor at the University of Texas at Austin.

"One of the challenges is that the term does not have a particular meaning," she said. "It mostly refers to policies that are favorable toward immigrants and generally suggesting that their employees or staff will not be participating in immigration enforcement."

‘Nobody can give me a definition’

So how does Dallas County Sheriff Lupe Valdez define it?

"First of all, nobody can give me a definition of sanctuary city," Valdez said. "Everybody has their own idea of what a sanctuary city is. My idea is somebody that saves you from everything — and Dallas will never be in that situation, or I don’t think any other city will be in that situation."

Valdez made headlines two years ago when she tweaked the rules about how long detainees are held at the county jail. Federal immigration officials can request that they be kept an extra 48 hours, until agents can get there.

The county had been sued for holding some detainees too long.

Abbott and others criticized her for releasing them too soon and not checking their documentation. He spoke with Fox News about the matter.

"It was the Sheriff of Dallas County who said she was not going to enforce laws against people who were seeking sanctuary," he said. "And when she saw what my order was on that, she quickly backtracked. All we're asking them to do is to follow and apply the federal law of the United States of America."

Valdez doesn't see it that way.

"I know there’s a misconception in this whole area that I don’t do that, but I do," she said. "I’ve always said: ‘If you come here to cause crime, you don’t belong here.’ As a matter of fact, I wish I could do something with the Americans who do that.

Valdez herself is a former Immigration and Customs Enforcement officer. The agency wouldn't comment on tape. Spokesman Carl Rusnok wrote in an email that ICE has an active working relationship with Dallas Sheriff's Office. And Valdez agrees.

"I don’t have any problem with ICE," she said. "We’ll continue turning over the people that ICE asked us for. ICE can’t afford to pick up 11 million people, they don’t have the time, resources, the place to put them, they don’t have any of that. So of course they’re going to ask for the people that they think are causing problems. Those are the ones we’re turning over, so what’s going to change?"

The Texas Tribune combed through ICE records in 2015. It found that Dallas County declined those federal requests just two times. That compares to 72 in Travis County and 11,000 in California.

Elissa Steglich points out that federal agents could've gotten the county to hold those two detainees by simply getting a warrant from a judge.

Still, Abbott and some legislators have an idea how to enforce compliance.

"To withhold funds from cities or counties declaring themselves to be sanctuary cities," he told Fox News.

Similar calls also came from Trump's campaign.

"What are they going to pull funding for?" Valdez asks. "Because I don’t comply with ICE? Go look at it. I comply with ICE. So then it would be easy for us, but no it doesn’t make any sense for them to try and do that."

That sets up round two of this battle in Austin. State Senator Charles Perry of Lubbock has revived his proposal to ban so-called "sanctuaries." And he has a powerful ally, Lt. Gov. Dan Patrick.

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