Mr. Sessions described the state’s so-called sanctuary laws as a radical maneuver that would threaten public safety and throw open the nation’s borders to even more illegal immigration.
Immigration law “is in the books, and its purposes are clear and just. There is no nullification, there is no secession. Federal law is the supreme law of the land,” said Mr. Sessions, one of the administration’s most adamant immigration restrictionists. He accused the state of intentionally using “every power the legislature has to undermine the duly established immigration laws of America.”
The lawsuit, which the Justice Department disclosed on Tuesday in advance of Mr. Sessions’s speech, capped a clash between the Trump administration and California that has lasted more than a year, with each side reaping political profit from the battle. The administration has sought to demonstrate that it will not tolerate noncompliance with federal immigration enforcement; California’s top officials, professed leaders of the anti-Trump resistance, have pushed the state to cooperate with Immigration and Customs Enforcement as little as possible.
Even as Mr. Sessions spoke, that opposition was making itself heard. Outside the hotel where Mr. Sessions was speaking, several hundred protesters marched, holding signs saying “Go Home Jeff” and “Crush ICE” and chanting, “What do we want? Sessions out!”
Shortly after Mr. Sessions’s speech, Mr. Brown and the state’s attorney general, Xavier Becerra, both Democrats, appeared together in the Capitol to denounce the lawsuit.
“California is in the business of public safety,” Mr. Becerra said. “We are not in the business of deportation.”
The suit, filed on Tuesday evening in Federal District Court in Sacramento, is the first Mr. Sessions’s Justice Department has filed against a local or state government over its immigration policies.
It targets three state laws passed in recent months: one that limits state and local agencies’ ability to share information about criminals or suspects with federal immigration officers, unless they have been convicted of serious crimes; a second that prohibits local businesses from allowing ICE to examine employee records without a court order or a subpoena; and a third that gave California officials more oversight over the state’s immigration detention centers.
Mr. Brown and Mr. Becerra defended the legislation as constitutional on Wednesday, saying that the laws prevented neither ICE agents from working in local jails and prisons nor employers from cooperating with ICE. The employee records law, Mr. Becerra said, simply ensures that workers and employers are guaranteed “their rights and their privacy and that those are being respected.”
Asked whether the law would, in effect, require warning undocumented workers to flee ahead of an ICE visit, Mr. Brown compared the provision to the practice of notifying criminal suspects that they have a right to a lawyer. “We are just following the law, and the law allows people to be advised of their rights,” Mr. Brown said. “Anything else smacks of a more totalitarian approach to things.”
Mr. Sessions had another comparison in mind.
What if, he asked, a state enacted legislation hampering the work of employees from the Occupational Safety and Health Administration or the Environmental Protection Agency? “Would you pass a law to do that?” he said.
Beyond the specifics of the laws, Mr. Sessions railed about several instances in which he said state officials had frustrated the work of federal law enforcement. He heartily ripped into Libby Schaaf, the Democratic mayor of Oakland, for issuing a warning last week that ICE planned to arrest immigrants across Northern California, an alert that infuriated agency officials who said her tip-off had allowed hundreds of their targets to slip away.
Ms. Schaaf’s actions “support those who flout the law and boldly invalidates illegality,” Mr. Sessions said, calling her warning “an embarrassment to the proud state of California.”
“So here’s my message to Mayor Schaaf,” he said. “How dare you, how dare you needlessly endanger the lives of our law enforcement officers to promote a radical open borders agenda?”
Ms. Schaaf said last week that she had not publicized any information that endangered ICE officers. She said she issued the warning because “I know that Oakland is a city of law-abiding immigrants and families who deserve to live free from the constant threat of arrest and deportation.”
Inside the hotel ballroom on Wednesday, Mr. Sessions faced a polite, if somewhat divided, audience.
Some police chiefs and sheriffs in liberal-leaning areas have argued that their agencies must distance themselves from ICE to avoid scaring off immigrant residents who may be more reluctant to serve as witnesses or come forward to report crimes. But there are many other officials across the country who say they would prefer to work with ICE if the legal issues surrounding such cooperation are clarified, and some who are eager to help the federal government outright with immigration enforcement.
Those tensions were palpable at Mr. Sessions’s speech, which was hosted by the California Peace Officers Association, a law enforcement advocacy group. The crowd responded to the speech with brief applause; about 10 of the more than 200 officers in the room stood to clap.
“I’m stuck in the middle,” said Deputy Chief Derek Williams of the police department in Ontario, a midsize city east of Los Angeles with a large Hispanic population. “It’s extremely bifurcated now.”
While the new state laws do not affect his work on a day-to-day basis, he said, the sharp increase in ICE activity has fostered “a lack of trust with law enforcement” among immigrant residents. “It’s a difficult time for us,” he said.
Among those who endorsed Mr. Sessions’s message was Paul R. Curry, a lobbyist for the California Correctional Supervisors Organization, which represents supervisors in the state prison system. He said California police chiefs were often caught between ICE’s requests and the orders of their mayors, who might embrace sanctuary policies.
“Every police officer is sworn to uphold the law not only of the state but the nation,” Mr. Curry said. “The progressive agenda is running afoul of the force of our laws in the country.”