WASHINGTON — President Donald Trump's warning that he would deploy the United States military to any state that refuses to take aggressive action against rioting rests on a longstanding presidential power that gives wide latitude to the White House, legal experts said.

But a decision to do so would be met with likely legal opposition and strong opposition from governors seeing it as an overreaction.

"If a city or state refuses to take the actions that are 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 during a Rose Garden address as cities across the country grappled with property destruction, looting and violent police clashes in the week since the death of George Floyd in Minneapolis.

Legal experts say the president does indeed have the authority under the Insurrection Act of 1807 to dispatch the military in states that are unable to put down an insurrection or are defying federal law. 

In the last half-century, presidents have sent the military to Southern states to ensure desegregation of schools and to protect civil rights in the 1950s and 1960s, and to Los Angeles after the California governor sought federal help during the 1992 riots.

Even so, the president's comments set up an immediate conflict with officials in some states, who disputed that the president had unilateral authority to send in troops against their will.

"The President of the United States is not a dictator, and President Trump does not and will not dominate New York state," New York Attorney General Letitia James said in a statement Monday, adding that the state was prepared to go to court if need be.

A leading Democratic voice on national security, Michèle Flournoy, who is a former top Pentagon policy official, said Tuesday that Trump should avoid using active-duty military forces except as a last resort.

"Most presidents, previous presidents, have understood the extreme sensitivity of using the U.S. military against American citizens or in confronting American citizens," Flournoy said at an online forum hosted by the Center for Strategic and International Studies.

Regarding the prospect of Trump invoking the Insurrection Act, she said, "He does have the authority. It's there for a reason. But if he manages this well, and if governors and mayors manage this well and use all the resources at their disposal, including the National Guard called up in a state capacity, it shouldn't be necessary."

The American Civil Liberties Union said it would be unnecessary to invoke the Insurrection Act — and irresponsible and dangerous.

"No level-headed governor is asking for an even more militarized response to civilian protests against police brutality and systemic racism — for good reason," said ACLU National Security Project Director Hina Shamsi.

Under the law, Trump would first have to proclaim that the insurgents disperse and retire peaceably within a certain amount of time. He could activate federal troops during an emergency without a governor's request as long as specific conditions are met, such as if the violence is interfering with the execution of laws in that state.

Stephen Vladeck, a national security and constitutional law expert at the University of Texas at Austin, said on Twitter that the federal government does not necessarily need a state request before using troops for domestic law enforcement, and that the Insurrection Act is open-ended in letting the president decide when circumstances merited its use.

He said the Insurrection Act had not been used since 1992, partly because of the unpopularity of using troops for domestic purposes.

"And it's hard to imagine courts second-guessing factual determinations by the President that circumstances warrant use of the military to restore order," Vladeck wrote. "Instead, the real constraint today might be responsibility; if Trump invokes these statutes, he'd own all that follows."

Not all experts are certain that the circumstances merit it.

Eugene Fidell, who teaches military justice at Yale Law School, said Monday that he does not believe Trump has the authority to send in troops without the governors' permission in these circumstances.

"Absent a request from the legislature or the governor of a state, I think the only way the power can be lawfully exercised is if there were an impeding of federal authority," he said, pointing to the example of Little Rock, Arkansas, when troops were sent in because the state was not abiding by a federal court order.

Kent Greenfield, a constitutional law professor at Boston College, said that what seems to distinguish this instance from many past ones — such as school desegregation clashes — is that there's no allegation that states are refusing to enforce federal law.

"The president is not asserting the right to enforce federal law. The president is asserting here the right to quell protests that are best left as a political matter and a prudential matter to the discretion of the states," Greenfield said.

He added, "He has the power to enforce his law, but he is not saying that the laws aren't being enforced. He is saying they're not being enforced the way he wants them to be enforced."