National Guard troops have been riding along on “most” of the immigration arrest operations ICE has attempted in Los Angeles over the last week, a top Homeland Security official said Monday, defending President Trump’s call-up of the National Guard.

Ernesto Santacruz Jr., director of U.S. Immigration and Customs Enforcement’s Los Angeles office, said the troops also are still defending federal buildings in the city from daily protests, and they are crucial to ICE being able to carry out the orders Mr. Trump has given.

He said the additional manpower has been “instrumental” in allowing ICE to do its job, and can’t be replaced by police.

“If these resources were not at my disposal, our immigration enforcement mission would be greatly impacted. The safety of our continued operations would be in doubt, placing both federal employees and the general public at an unnecessarily greater risk,” Mr. Santacruz said.

He said local police are working hard, but the National Guard assistance is “unparalleled.”

His declaration came as Justice Department lawyers defended Mr. Trump’s troop deployment to the 9th U.S. Circuit Court of Appeals, urging the judges to block a lower court ruling that ordered Mr. Trump to relinquish control of the National Guard troops back to California Gov. Gavin Newson, who wants them to stand down.

The court is scheduled to hear oral argument Tuesday.

The protests began more than a week ago and, while they have cooled somewhat, they are still disrupting ICE as it tries to conduct immigration operations, the Trump administration said.

In one instance Saturday, more than 1,000 protesters gathered outside a federal building and courthouse in Los Angeles, hurling rocks and bricks and firing “commercial-grade fireworks” at ICE. Protesters also blocked an exit, preventing ICE from transporting 130 detainees.

It took National Guard troops to clear a path so the detainees could be moved, Mr. Santacruz said.

And the Guard members’ presence has prevented other situations from flaring up, he said.

“Having the National Guard at our fingertips as a Quick Reaction Force is key to maintaining officer safety and continuing our immigration enforcement operations,” he said.

As of Saturday, there were 4,155 Guard members, 821 active-duty Marines and 382 vehicles involved in the federal military effort, according to Major Gen. Scott Sherman, commander of the Army’s Task Force 51.

He said they are guarding a federal courthouse, an ICE facility and several other locations where federal employees maintain a presence.

Guard members are also escorting ICE deportation officers and other federal law enforcement personnel who are helping them as they pursue at-large illegal immigrants for arrest.

Protection is provided to enable federal law enforcement officers to conduct their federal functions safely and with minimal interference from bystanders, officials said.

Gen. Sherman said the federalized troops haven’t detained anyone as part of their duties. He said a Marine did detain one person who kept trying to enter a restricted area even after warnings to stop. That person was placed in cuffs and turned over to local police.

One Guard member has been injured. Gen. Sherman said the soldier was holding a riot shield when a protester grabbed it, pulled it down and then let go. The shield sprung up into the soldier’s mouth, chipping his tooth.

Mr. Newsom says Mr. Trump broke the law by going around him to call up the National Guard.

U.S. District Judge Charles Breyer agreed. The judge said Mr. Trump did not act “through” the governor. He also said the call-up violated the Constitution’s 10th Amendment, which guarantees states some measure of autonomy.

Anna Mohan, the Justice Department lawyer who led Monday’s filing with the appeals court, said Judge Breyer’s attempt to second-guess the president’s decision-making was itself unconstitutional.

She said the Supreme Court established nearly 200 years ago that authority to call out the militia — what is today the National Guard — must belong “exclusively” to the president.

• Stephen Dinan can be reached at sdinan@washingtontimes.com.