The Trump administration on Monday ordered the deployment of U.S. Marines to Los Angeles and intensified raids on suspected undocumented immigrants. The move fuelled more outrage from street protesters and Democratic leaders, who raised concerns over a national crisis.

Officials said about 700 Marines based in Southern California were expected to reach Los Angeles Monday night or Tuesday morning. The deployment was part of a federal strategy to quell street demonstrations opposing the immigration raids, which were part of President Donald Trump’s second-term efforts.

Although the Marines’ mission to protect federal personnel and property was temporary, it filled the gap until a full contingent of 4,000 National Guard troops could reach Los Angeles. The deployment marked an extraordinary use of military force in support of a police operation has come under severe criticism from the state and local leaders who had not requested help.

Meanwhile, U.S. Homeland Security Secretary Kristi Noem pledged to carry out even more operations to round up suspected immigration violators, extending a crackdown that provoked the protests. Trump officials branded the protests as lawless and blamed state and local Democrats for permitting upheaval and protecting undocumented immigrants in sanctuary cities.

The military and federal enforcement operations further polarised America’s two major political parties. Trump, a Republican, threatened to arrest California’s Democratic governor, Gavin Newsom, for resisting the federal crackdown.

California sued the Trump administration to block the deployment of the National Guard and the Marines on Monday, arguing that it violated federal law and state sovereignty.

The top Democrat on the Senate Armed Services Committee, Senator Jack Reed, said he was “gravely troubled” by Trump’s deployment of active-duty Marines.

“The president is forcibly overriding the authority of the governor and mayor and using the military as a political weapon. This unprecedented move threatens to turn a tense situation into a national crisis,” Reed said.

“Since our nation’s founding, the American people have been perfectly clear: we do not want the military conducting law enforcement on U.S. soil,” he said.

The announcement that Marines would be deployed was made on the fourth straight day of protests. Late on Monday, police began to disperse hundreds of demonstrators who gathered outside a federal detention centre in downtown Los Angeles, where immigrants had been held. Police said arrests were being made.

National Guard forces had formed a human barricade to keep people out of the building. Then a phalanx of police moved up the street, pushing people from the scene and firing “less lethal” munitions such as gas canisters. Police had used similar tactics since Friday.

U.S. Marines were known as the first American forces to establish a beachhead in U.S. military interventions, and as the last forces to leave any occupation.

Though military forces had been deployed domestically for major disasters such as Hurricane Katrina and the attacks of September 11, 2001, it was extremely rare for troops to be used domestically during civil disturbances.

Even without invoking the Insurrection Act, Trump could deploy Marines under certain conditions of law or under his authority as commander in chief.

The last time the military was used for direct police action under the Insurrection Act was in 1992, when the California governor at the time asked President George H.W. Bush to help respond to the Los Angeles riots over the acquittal of police officers who beat Black motorist Rodney King.

Newsom contended it was his charge as governor to call in the National Guard, labelling Trump’s action as “an unmistakable step toward authoritarianism.”

Trump in turn, said he supported a suggestion by his border czar Tom Homan, that Newsom should be arrested over possible obstruction of his administration’s immigration enforcement measures. “I would do it if I were Tom. I think it’s great,” Trump told reporters.

The protests so far have resulted in a few dozen arrests and some property damage.

“What is happening affects every American, everyone who wants to live free, regardless of how long their family has lived here,” said Marzita Cerrato, 42, a first-generation immigrant whose parents were from Mexico and Honduras.

Protests also sprang up in at least nine other U.S. cities on Monday, including New York, Philadelphia and San Francisco, according to local news outlets.

In Austin, Texas, police fired nonlethal munitions and detained several people as they clashed with a crowd of several hundred protesters.

Before the Los Angeles dispersal, several hundred protesters outside a detention centre chanted “free them all,” flew Mexican and Central American flags, and directed sometimes-vulgar insults toward federal officers.

At dusk, officers had confrontations with protesters who had scattered into the Little Tokyo section of the city. As people watched from apartment patios above street level and as tourists huddled inside hotels, a large contingent of LAPD officers and sheriff’s deputies fired several flash bangs that boomed through side streets along with tear gas.

Homeland Security said its Immigration and Customs Enforcement division had arrested 2,000 immigration offenders per day in recent days, far above the 311 daily average in fiscal year 2024 under former President Joe Biden.

“We conducted more operations today than we did the day before and tomorrow we are going to double those efforts again,” Noem told Fox News’ “Hannity.” “The more that they protest and commit acts of violence against law enforcement officers, the harder ICE is going to come after them.”

Los Angeles Mayor Karen Bass opposed the clampdown, telling MSNBC, “This is a city of immigrants.” Noem countered that, “They are not a city of immigrants. They’re a city of criminals.”