Attorney General Jeff Sessions took his war against sanctuary cities to California on Wednesday, announcing a federal lawsuit against the state and attacking its elected officials as “radical extremists” in the state’s capital city.

In a speech laden with tough rhetoric for his critics and immigration advocates, Sessions decried officials who support so-called sanctuary city policies as “extremists” promoting “open borders.”

“Stop treating immigration agents differently from everybody else for the purpose of eviscerating border and immigration laws and advancing an open borders philosophy shared by only a few, the most radical extremists,” Sessions said.

Sessions had harsh words in particular for Oakland Mayor Libby Schaaf, who recently announced publicly that federal authorities would be conducting immigration crackdowns in her area. That move has been heavily criticized by immigration officials, who allege she’s responsible for hundreds of criminals avoiding capture.

“Her actions support those who flout our laws and boldly validates illegality,” Sessions said. “There’s no other way to interpret those remarks.”

“So here’s my message to Mayor Schaaf: How dare you?” Sessions continued. “How dare you needlessly endanger the lives of law enforcement to promote an open borders agenda.”

The attorney general’s speech in Sacramento at a state law enforcement gathering came on the heels of a move by the Justice Department late Tuesday to sue California over its so-called “sanctuary” policies that prohibit some cooperation with federal immigration enforcement.

The move is an aggressive escalation of a battle the administration has been waging since President Donald Trump’s inauguration to pressure local jurisdictions to help the feds catch undocumented immigrants.

Sessions defended the lawsuit, saying it was about preventing “nullification” of federal laws, which he compared to the secessionist movement during the Civil War.

“Contrary to what you might hear from the lawless open-borders radicals, we are not asking California, Oakland, or anyone else to actually effectively enforce immigration laws,” Sessions said.

“I can’t sit by idly while the lawful authorities of federal officers are being blocked by a legislative action of politicians,” he added.

States and cities say their policies are protecting the best interest of their citizens and say they should not have to spend their limited resources on a federal responsibility.

California Gov. Jerry Brown said the lawsuit was a stunt.

“At a time of unprecedented political turmoil, Jeff Sessions has come to California to further divide and polarize America. Jeff, these political stunts may be the norm in Washington, but they don’t work here. SAD!!!” the Democratic governor tweeted.

Sessions defended the Trump administration’s push on undocumented immigrants, stressing that it wants to focus on legal immigrants. The US welcomes over 1 million immigrants a year legally by giving them green cards, more than any other nation, he said.

“And let no one contend that we reject immigration and want to ‘wall off America’ from all immigrants,” Sessions said. “Indeed, at this unprecedented rate, we will soon have the largest percentage of non-native born in our nation’s history, and the percentage is continuing to rise every year thereafter.”

The lawsuit is the latest broadside from the Trump administration against so-called “sanctuary cities” — a broad term referring to localities that abide by some measure of non-cooperation with federal law enforcement though previous courts have blocked many of the administration’s efforts to pressure sanctuary jurisdictions, with federal judges siding with those cities and states in litigation.

Sessions said Wednesday he expects to prevail in this case.

“California, (it) absolutely appears to me, is using every power it has — powers it doesn’t have — to frustrate federal law enforcement. So you can be sure I’m going to use every power I have to stop them,” Sessions said.

“We are going to fight these irrational, unfair, unconstitutional policies that have been imposed on you and your officers or our federal officers. … And we intend to win this fight.”