Legal experts regard the act as a major exception to the law that generally forbids the use of the military for domestic law enforcement.
President Donald Trump threatened Monday (Tuesday NZ time) to use federal forces to quell the protests and violence that have swept the country, a measure that would require the use of an 1807 law called the Insurrection Act.
"If a city or state refuses to take the actions necessary to defend the life and property of their residents, then I will deploy the United States military and quickly solve the problem for them," Trump said in the Rose Garden.
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Although he did not mention it by name, Trump would be invoking the Insurrection Act, legal experts said, which is a group of statutes approved by Congress in the early 1800s that gives the president the power, under some conditions, to activate federal troops for domestic law enforcement.
What is the Insurrection Act?
An early version of the Insurrection Act was first approved by Congress in 1792 to "provide for calling forth the militia to execute the laws of the union, suppress insurrections and repel invasions." It has been amended several times in the centuries since.
Generally, the law gives the president the power to send military forces to states to quell widespread public unrest and to support civilian law enforcement. But before invoking it, the president must first call for the "insurgents" to disperse, according to a Congressional Research Service report published in 2006. If stability is not restored, the president may then issue an executive order to deploy troops.
The idea for the law was that there could be circumstances in which the local and state authorities were either unable or unwilling to maintain order, said Stephen I. Vladeck, a law professor at the University of Texas School of Law. In those cases, the military would be the backstop.
What is its relationship to state governments?
The use of the military for civilian law enforcement has been restrained as part of the Constitution's protections for civil liberties and state sovereignty. State governments maintain the authority to keep order within their borders, a power given to them under the Posse Comitatus Act of 1878.
Generally, that law forbids the use of the military as a domestic police force.
But the Insurrection Act authorises the president to use the military to suppress an insurrection if a state government requests it. And there is some leeway in the president's discretion, such as if the commander in chief considers that the unrest is obstructing US laws.
What are previous examples of its use?
The last time that the act was used was in 1992, when riots in Los Angeles broke out after four white police officers were acquitted in the beating of Rodney King, a black motorist. Armed forces have also been used to quell civil disturbances after natural disasters, such as in widespread looting in St. Croix, in the US Virgin Islands, after Hurricane Hugo in 1989, according to the Congressional Research Service report.
These statutes were used regularly throughout US history.
Vladeck said in an email Tuesday that the statutes were employed in conflicts with Native Americans along the 19th-century frontier; during industrial strife in the late 19th century and the early 20th century; and to enforce federal court orders requiring desegregation during the civil rights movement.
Kent Greenfield, a constitutional law professor at Boston College, told The Associated Press that, in Trump's case — and unlike the clashes over school desegregation — there was no allegation that states were refusing to enforce federal law.
"He is not saying that the laws aren't being enforced," Greenfield said of the president. "He is saying they're not being enforced the way he wants them to be enforced."
Vladeck said that politics also played a role in whether presidents used the act.
"The Insurrection Act hasn't been invoked since 1992 — largely because domestic use of the military is generally unpopular," he wrote on Twitter last week.
Could the president's use of the Insurrection Act be opposed?
Originally, the statutes set clearer limitations, like a sunset provision for the use of military forces, and a required judicial review, Vladeck said.
But after those provisions were repealed, it became "somewhat unclear how an abuse of the statute could be reined in," he said.
"We've been lucky, historically, that political considerations have prevented presidents from abusing these authorities," he said. "But there is no guarantee that comparable considerations would restrain President Trump."
Although the president does not need a request from a state to use federal armed forces for domestic law enforcement under the Insurrection Act, some experts do not believe the current circumstances justify such a deployment without the agreement of the state governor or legislature.
Eugene R. Fidell, a senior research scholar at Yale Law School, said such a move would be "litigated and litigated quick."
"To the extent that there is wiggle room and a judgment call to be made, the question is how much a margin of appreciation would a federal court afford him," Fidell said.
He said there would have to be a "catastrophic decapitation" of law enforcement and civil government in the state to warrant that deployment. "You are talking about an unprecedented situation of utter chaos and a complete collapse," he said. "At that point, all gloves are off.
"But there is nothing like that going on," he added.
Several governors have said they oppose the president sending federal troops into their states. Governor Tim Walz of Minnesota, whose state has been at the center of the protests, has declined Trump's offer of a military police response in his state.
Governor Andrew Cuomo of New York said in an interview Monday with CNN host Erin Burnett that he would say, "thank you, but no thank you."
Governor J.B. Pritzker of Illinois, a Democrat, also told CNN that he would not request military assistance. "I reject the notion that the federal government can send troops into the state of Illinois," he said.
"The fact is that he should stay out of our business," the governor said. "We are working hard in the state of Illinois to bring down tensions."
Written by: Christine Hauser
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