Here’s what it takes to become a sanctuary city: You, or someone else, starts calling your city a sanctuary city.
That is, there’s no one policy or criteria that makes a place a sanctuary city.
So when President Donald Trump announced in an executive order  Wednesday that he’d withhold federal grant money from sanctuary cities, it wasn’t immediately clear who he was talking about, or what criteria he’d use to identify offending locales.
Places that are considered sanctuary cities might be ones that prohibit their jails from inquiring about immigration status, refuse to alert Immigration and Customs Enforcement when an undocumented immigrant will be released from custody or decline to assist with other enforcement activities.
The language from Trump’s order is impossibly vague, and includes any entity with “a statute, policy, or practice that prevents or hinders the enforcement of Federal law.”
Whatever definition the administration uses could matter quite a bit, since San Diego has popped up on lists of sanctuary cities for years even as its leaders insist it isn’t one.
A separate order signed by Trump on Wednesday could impact San Diego bigly as well – it’s the one greenlighting a border wall and related enforcement and detainment actions.
For example, that order suggests criteria for those seeking asylum will become more strict, which has implications for the thousands of asylum-seekers crowding Tijuana . And it calls for the immediate construction of facilities “to detain aliens at or near the land border with Mexico.”
Plenty of websites have compiled lists of sanctuary cities, and San Diego lands on many of them. But the mayor’s office has said San Diego is not one.
Mayor Kevin Faulconer’s staff told City News Service in 2015 that despite San Diego being listed as a sanctuary city on various online resources, there’s no specific law or policy making it one – and that the city does work cooperatively with federal immigration authorities.
Faulconer vowed in his 2015 State of the City  address to support comprehensive immigration reform, which should include a path to citizenship. The City Council unanimously supported any plan that included that. Faulconer’s criticism of Trump’s border rhetoric more recently, however, has centered on commerce and trade rather than immigration policy:
SD already has a border built by the Feds. Crossborder trade creates jobs. Our binational economic & cultural ties have my full support.
— Kevin Faulconer (@Kevin_Faulconer) January 25, 2017 
A separate order  signed by Trump Wednesday deals with a policy known as 287(g), which allows local law enforcement officers to act as immigration enforcement. Trump wants police agencies to use 287(g); President Barack Obama did not.
When the Union-Tribune asked San Diego Police Chief Shelley Zimmerman in November about whether the department would implement the program , she didn’t answer the question directly.
Her statement does, however, explain why supporters of sanctuary policies believe the designation is crucial: Immigrants might be dissuaded from reporting crimes if they believe contact with police officers will lead to their deportation.
“The San Diego Police Department does not check the immigration status of victims and witnesses of crimes to encourage all people to come forward, confident in the knowledge their report will be investigated thoroughly and professionally,” Zimmerman told the U-T.
Assemblywoman Lorena Gonzalez, whose district runs along the U.S.-Mexico border and also includes refugee-heavy communities in City Heights, said this is one of her biggest worries regarding Trump’s action.
“For decades, our police officers have worked very hard to have this relationship with immigrant communities, and there is a certain trust there. What he’s done today is breaking that up,” she told me. “If you’re a victim of a crime, the most unsafe thing we could do is to allow police” to arrest the very people who step forward to make a report.
The California State University system, which includes San Diego State, doesn’t use the word “sanctuary,” but last year declared  it won’t cooperate with any federal policies that zero in on undocumented students. The University of California announced similar policies , and the University of San Diego’s president said he would form a task force to explore the issue .
San Diego County is home to 743,500 immigrants, according to a report from the Immigrant Legal Resource Center . We don’t know how many are undocumented.
The San Diego County Sheriff’s Department, the law enforcement authority for unincorporated parts of the county and some smaller cities, does cooperate with federal immigration authorities. The report found San Diego County to be among jurisdictions that “spend substantial local time and resources on civil immigration enforcement.”
The Sheriff’s Department, for example, allows what are called detainers – requests from Immigration and Customs Enforcement to hold an immigrant after he or she is supposed to be released, so ICE can detain them.
Other cities in the county have varying policies. Escondido has earned a reputation as one of the toughest cities in the country on immigrants , while National City Mayor Ron Morrison has said  the city is not a sanctuary city but that when it comes to undocumented immigrants, police there don’t “hunt them down or turn them in.”
California could be considered a sanctuary state, if that was a thing.
The state’s TRUST Act went into effect in 2014, and limits the ways in which local jails can hold people in order to turn them over to immigration officials. In most cases, local law enforcement can’t hold those who’ve been arrested for minor crimes, including most traffic offenses.
Trump’s actions come one day after California leaders celebrated their intentions to fight him on precisely these types of efforts. Gov. Jerry Brown was unusually forceful in his State of the State address Tuesday, where he said “immigrants are an integral part of who we are and what we’ve become” and vowed to protect them. California Attorney General Xavier Becerra, who was sworn in Tuesday, has expressed support for sanctuary cities. (Disclosure: My husband works for the California Department of Justice.)
San Diego Sen. Joel Anderson cited that as the reason he declined to support Becerra’s nomination. “Californians deserve better than a top law enforcement officer who wants to protect illegal alien drunk drivers. As a supporter of sanctuary cities, that’s exactly what Congressman Becerra wants to do,” Anderson said in a statement before Becerra was sworn in.
Other San Diego legislators, however, condemned Trump’s order.
One, Sen. Ben Hueso, who is chair of the state’s Latino Caucus, already introduced a bill this session that would give legal representation to immigrants facing deportation proceedings .
“Building walls is a failed political policy that should remain in medieval history,” Hueso said in a statement.
So when state officials say they want to limit or fight Trump’s order, what exactly do they mean?
For one, “We’re going to defend the things we’ve passed, like the TRUST Act,” Gonzalez said. She said for now, she expects the fight to take place in court – and in Congress. Indeed, the leader of the California Senate suggested a court battle was inevitable:
Cutting off funds for cities that refuse destructive deportation programs is unconstitutional. See you in court. https://t.co/NjGfZfvMrd 
— Kevin de Leόn (@kdeleon) January 25, 2017 
Others have suggested that Trump is goading California into a legal challenge it can’t win .
“We don’t know how they can keep money from coming to California – it’s our money. We do know that the president can’t do this on his own,” Gonzalez said. “Funds have to be appropriated through Congress, there’s more action that would happen to make this work.”
Gonzalez said former Attorney General Eric Holder, who has been hired by California to help push back against Trump administration policies, will be exploring whether his immigration actions represent a violation of the 10th Amendment to the U.S. Constitution, which prohibits the federal government from forcing states to provide resources or personnel for federal enforcement actions.