Political and policy differences can put local and federal officials on opposing sides. A current example involves whether to protect or deport foreign-born U.S. residents who lack immigration documents. Some mayors, councils and police chiefs don't help federal agents find deportation targets as the Trump administration looks fort them more aggressively. The top elected official in Oakland, Calif., goes further by warning about upcoming raids and recommending a local group that provides lawyers for detained immigrants.

Mayor Libby Schaaf, a Democrat elected in 2014, says she issued an alert Feb. 24 to protect residents from arrest and being sent to Mexico or Latin America. "I felt it was my duty to share the information I had," Schaaf says. "It was legal what I did and it is important that people know their rights." Under a new law signed by Gov. Jerry Brown, California is a "sanctuary state." That greatly limits who state and local law enforcement agencies can hold, question and transfer at the request of federal authorities. (More than 2.3 million immigrants without visas or work permits are believed to be in California.) Boston and other cities around the country have similar sanctuary policies, and some religious centers offer to shield immigrants from arrest.

On the other side, the president's secretary of homeland security, Kirstjen Nielsen, suggests that local actions such as Mayor Schaaf's are "putting my officers at risk." Thomas Horman, acting director of Immigration and Customs Enforcement (ICE), sharply criticizes the mayor's recent heads-up: "It's beyond the pale. I've been doing this for 34 years and this is a whole new low -- to intentionally warn criminals that law enforcement is coming. I just can't believe it happened. . . . And there's 800 that we were unable to locate because of that warning." Trump administration supporter Tucker Carlson, a Fox News host, says what Mayor Schaaf did "is like telling bank robbers the cops are on the way."

California Democrat says: "What I did was my job as the mayor of Oakland and reflective of the values of the people that I represent. . . . I do not regret sharing this information." -- Libby Schaaf

Republican lawyer says: "The Constitution and the Supreme Court are quite clear -- immigration law is the sole preserve of the federal government." – John Yoo, past White House legal adviser

Commentator says: "Under the Trump administration, an ugly deportation force has been indiscriminately terrorizing immigrant and Latino communities. Schaaf is rightly and lawfully acting on her conscience to resist the intrusion by the feds into state and local law enforcement." – Raul Reyes, New York City lawyer and columnist