The most far-reaching change of all is a bill known as the Trust Act, which prohibits law enforcement officers from turning over persons they detain to immigration authorities except in arrests for major felonies or sex crimes. Law enforcement objected to a more expansive version of this measure, which Brown obligingly vetoed in 2012. This year he worked with the bill’s authors to get a version acceptable to police and prosecutors; the enacted measure largely follows the practice of the Los Angeles Police Department, the state’s largest police force.

The LAPD, and many other police agencies, resent being used as arresting officers by the U.S. Immigration and Customs Enforcement agency, better known as ICE. Police say they need support in immigrant communities to do their jobs of protecting the public and that this won’t happen if residents fear that cooperation would make them subject to questioning—or deportation—by federal authorities.

No one knows with certainty how many people will be affected by the Trust Act, but the number runs into the scores of thousands. Despite recently easing its policies, the Obama administration has deported nearly 2 million illegal immigrants, more than were deported during the entire two terms of the George W. Bush administration. One estimate says that 100,000 such residents were picked up last year in California alone and turned over to ICE. It is not known how many of them were detained for minor offenses, but the issue is a touchy one in immigrant circles since many in this group have U.S. family ties.