Alan Gomez

USA TODAY

President Trump signed an executive order Wednesday directing the government to identify federal money it can withhold to punish "sanctuary cities" — a term for up to 300 communities that have policies protecting the nation's 11 million undocumented immigrants from deportation.

Trump vowed to "crack down" on those cities during a speech at the Department of Homeland Security.

"These jurisdictions have caused immeasurable harm to the American people and to the very fabric of our Republic," Trump's executive order said.

A showdown between Trump and local governments over "sanctuary cities" likely will result in legal challenges testing how far the White House can go in dictating its priorities.

Trump orders clamp down on immigrant 'sanctuary cities,' pushes border wall

Trump will be armed with a range of powerful options, including federal lawsuits and the power to withhold hundreds of millions of dollars in grants that states and cities rely on.

"The Trump administration can largely get the results it is seeking and a real meaningful end to most of these sanctuary policies through a combination of carrots and sticks," said Jessica Vaughan, director of policy studies at the Center for Immigration Studies, who has advised the Trump transition team on immigration enforcement options. "The point is not to go around whacking all these little cities and counties, it's to get them to do the right thing. And for the die-hards, to confront them."

Local communities are digging in for a fight. Chicago Mayor Rahm Emanuel created a task force to help undocumented immigrants and pledged $1 million for a legal defense fund. "Chicago always will be a sanctuary city," he said.

Some cities — including San Francisco, Chicago and New York — proudly declare themselves sanctuaries and have enacted policies that prohibit municipal employees from turning over residents or information on them to the U.S. Immigration and Customs Enforcement (ICE).

Other cities more narrowly restrict police from inquiring about the immigration status of detained suspects. There also are cities that work with federal immigration authorities but refuse to hold suspects in jail solely so ICE agents can pick them up.

Beyond city governments, institutions that include churches and universities vow to fight federal efforts to round up undocumented immigrants on their grounds.

Here are the two most powerful weapons the Trump administration will have to fight back:

LAWSUITS

If Sen. Jeff Sessions, R-Ala., one of the most outspoken critics of illegal immigration, is confirmed as attorney general, he will be able to sue cities on the grounds they are violating federal law by refusing to cooperate with immigration enforcement.

Theresa Cardinal Brown, director of immigration policy at the Bipartisan Policy Center, said that kind of lawsuit fits Trump's "big and showy style," but the law is murky.

The Justice Department under the Obama administration ruled last summer that local law enforcement agencies are required by federal law to at least share that information. However, the 3rd U.S. Circuit Court of Appeals in Philadelphia ruled in 2014 that local police departments are not required to hold undocumented immigrants for ICE.

"Justice could spend all of its time and resources going after these cases," Brown said.

GRANT MONEY

The two most likely federal agencies that could cut off funding are Justice and Homeland Security. They provide grants for local law enforcement agencies to hire officers; bolster prosecutions, courts and jails; provide drug treatment, prepare for terrorist attacks, and assist crime victims and witnesses.

The Trump administration has the power to cut off much of that funding. For example, Justice's State Criminal Alien Assistance Program, or SCAAP, distributed $165 million in 2015 to local agencies that detained undocumented immigrants in its jails.

Laurie Robinson, a former assistant attorney general under Presidents Clinton and Obama who headed the Office of Justice Programs, which oversees grants, said the statute implementing SCAAP gives an attorney general broad power to decide who gets money.

"They could cut off drug programs, domestic violence grants, violence against women grants," she said.

Other grants won't be as easy to end. Justice's Community Oriented Policing Services program distributed $208 million in 2015 to local agencies. But that money is distributed using a formula established by Congress, meaning an attorney general can't revoke grants without lawmakers' approval.

"Unless Congress were to change something, the executive branch cannot really decide on its own to cut off a grant that is by statute designated to go to a local jurisdiction," said Robinson, now a criminology professor at George Mason University.

Help won't be hard to find. Republicans in Congress, including Rep. Duncan Hunter of California and Sen. Pat Toomey of Pennsylvania, have tried in recent years to pass laws establishing those kinds of cuts, but they always faced a veto threat from Obama. Republicans filed similar bills this week, and those have a far better chance of becoming law now that Republicans control Congress and the White House.

Rosemary Jenks, director of government relations for NumbersUSA, which favors lower immigration levels, said it's impossible to know how nasty the fight will get over sanctuary cities given the raw emotions on both sides. "I'm not going to rule anything out," she said.