President-elect Donald Trump made attacking sanctuary cities, like San Francisco, a cornerstone of his campaign. 

"We will end the sanctuary cities that have resulted in so many needless deaths. Cities that refused to cooperate with federal authorities will not receive taxpayer dollars," he told a cheering crowd during an August stump speech. 

Since Trump's election, there's been a lot of hand-wringing over what that could cost some of the nation's most liberal and biggest cities: Los Angeles, Chicago and New York are all among the jurisdictions with sanctuary policies.

But could a Trump administration and Republican Congress really withhold money from  those cities or even entire states like California? The answer -- from lawyers on both sides of the debate -- is a lot more nuanced than Trump's rhetoric lets on.

A Sanctuary City By Any Other Name

First things first: What is a sanctuary city?

Angela Chan, senior staff attorney at Asian Americans Advancing Justice-Asian Law Caucus, an immigrant rights firm in San Francisco, says there's no uniform definition.

"Maybe one kind of vague and broad definition is when a city ... decides to limit their use of their local resources and local personnel from immigration enforcement," said Chan. 

That’s one thing Chan and Jessica Vaughan actually agree on. Vaughan works for the Center for Immigration Studies, a think tank that supports more restrictive immigration policies. She’s among those who support Trump’s call for punishing jurisdictions that embrace these policies.  We asked her: How many exist?

"There are just over 300 of these jurisdictions, and they range from cities and towns to counties. And even a couple of states have sanctuary policies," Vaughan said. 

The History of Sanctuary in California

That’s right -- entire states. And California is one of them, because of a 2013 law known as the Trust Act. It limits when California jails are allowed to cooperate with ICE, and lets them go farther than the state limits if they want. The Trust Act was enacted after the federal government started requiring local jails to share the fingerprints of anyone they book into custody -- and keep them behind bars if Immigration and Customs Enforcement, or ICE, deemed them eligible for deportation.

"The Trust Act not only allows local jurisdictions within California to have egregious sanctuary policies, but it also restricts the cooperation of even those sheriffs, for example, who would like to be able to work with ICE," said Vaughan.

Sanctuary policies actually began back in the 1980s, when leaders in some cities, including Los Angeles and San Francisco, were moved to protect Central Americans fleeing civil wars after the Reagan administration refused to give them asylum. But most were adopted in recent years after ICE started asking local jails to hold undocumented people, even if they were otherwise eligible for release.

Supporters say the policies make for safer communities, because immigrants are more likely to trust and cooperate with local governments if they’re not afraid of being deported.  But critics say they are just protecting criminals, like the man accused of shooting Kate Steinle on a San Francisco pier last year.

Money, Money, Money

 Vaughan believes cities, counties and states that don’t cooperate with those detainer requests are flouting federal law and could be punished under a Trump administration.

"There are a number of tools the federal government has to use to address the sanctuary jurisdiction problem. The first, and most obvious one, is block these jurisdictions from getting certain types of federal funds," she said. 

She doesn’t think that San Francisco, for example, would immediately lose all $1 billion it receives each year in federal funding. But the Trump administration could try to cut law enforcement grants by executive action, she said -- something the Obama administration has already done. Vaughan said that under Obama, the Department of Justice has blocked 10 jurisdictions, including the state of California, from applying for certain grants because they have policies that are inconsistent with federal law.

"The array of grant programs that could become off-limits could be expanded, and if that happens I believe a lot of these jurisdictions are going to revisit their policies and begin to cooperate," Vaughan said.

So perhaps San Francisco could be at risk of losing up to $35 million that it gets annually in law enforcement assistance from the feds.

Taking It to the Courts

And what if sanctuary jurisdictions dig in and refuse to change their policies, as leaders up and down the state of California have vowed to do?

"In that situation, the federal government needs to look at litigation against those jurisdictions and possibly even prosecution," said Vaughan.

Chan, the immigration rights lawyer, agrees that the fight will likely end up in court. But she thinks jurisdictions who refuse to cooperate with immigration holds are actually on strong legal footing.

"The new Trump administration can make a lot of threats and boasts, as they do, but there are limits to what they can force localities to do," she said.

Chan says federal courts have already ruled that forcing local jails to hold someone, based on an ICE hold, violates Fourth Amendment rights against unreasonable seizures. In fact, she said, some counties have adopted sanctuary policies to protect their sheriff's departments from being sued for illegally detaining people. 

"Federal courts have said you can't have an unreasonable seizure, and an unreasonable seizure of a body is when it's not based on probable cause or a warrant signed by a judge," Chan said. "On top of that, there was a recent court decision from Illinois saying ... that ICE is going outside of the bounds of what federal statute allows because they are issuing these (hold requests) willy-nilly, they are not issuing them based on someone's flight risk. These are just ICE agents signing detainers. They are not based on any judiciary review or any gathering of probable cause evidence."

Chan said there are also two Supreme Court decisions that could limit a Trump administration’s ability to withhold federal funding. Both were suits brought by conservative plaintiffs seeking to limit local cooperation with federal laws -- one dealing with gun control and one dealing with the Affordable Care Act. And in both cases, the Supreme Court ruled in favor of states' rights.

"I think states' rights cut both ways -- progressively in terms of defending immigrants, and it cuts conservatively in pushing back against gun control or expanded health care," said Chan.

Vaughan argues the Trump administration would ultimately prevail if these issues were litigated. But she and Chan agree on the timeline: California shouldn’t expect federal assistance to suddenly disappear come Jan. 20.