Marines, raids and protest further polarise US politics

The Trump administration has ordered US Marines into Los Angeles and intensified raids on suspected undocumented immigrants, fueling more outrage from street protesters and Democratic leaders who raised concerns over a national crisis.

Some 700 Marines based in Southern California were expected to reach Los Angeles on Monday night or Tuesday morning, officials say, as part of a federal strategy to quell street demonstrations opposing the immigration raids, which are a part of a signature effort of President Donald Trump's second term.

Although their mission to protect federal personnel and property is temporary - filling the gaps until a full contingent of 4000 National Guard troops can reach Los Angeles - the deployment is an extraordinary use of military force in support of a police operation, and it comes over the objection of state and local leaders who did not request help.

Meanwhile, US 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 have branded the protests as lawless and blamed state and local Democrats for permitting upheaval and protecting undocumented immigrants with sanctuary cities.

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

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

The top Democrat senator on the Senate Armed Services Committee, 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 US 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 have 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.

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

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

Even without invoking the Insurrection Act, Trump can 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 Los Angeles riots over the acquittal of police officers who beat Black motorist Rodney King.

Newsom contends it is 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.

Protests also sprang up in at least nine other US 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.