How Trump could use the military to go after the 'radical left'

Former President Donald Trump says active-duty or National Guard troops could be used to go after "radical left lunatics" to handle any Election Day chaos, warning that the bigger problem facing the United States isn't a foreign enemy but "the people from within."

The suggestion of using military force following a political election is hypothetical, considering Trump won't have command of U.S. troops in November. If he wins the election, Trump wouldn't gain control of the armed forces until mid-January following the inauguration.

But deploying the military within U.S. borders is a suggestion Trump has made before, including the idea that the military could police the southern border and help deport an estimated 11 million undocumented immigrants in the United States.

"I think the bigger problem are the people from within," Trump told Fox News' "Sunday Morning Futures."

"We have some very bad people. We have some sick people, radical left lunatics... And it should be very easily handled by, if necessary, by National Guard or really necessary by the military, because they can't let that happen," he said.

So, can a president use U.S. troops to police Americans and quash political protests?

Many of Trump's supporters say yes, citing a 200-year-old law meant to curb rebellions. The Insurrection Act of 1807 was used during the Civil War and throughout the 1960s to enforce civil rights laws.

Legal experts are now warning the law is dangerously vague and ripe for abuse.

Here's what to know about the use of military power on U.S. soil:

The military is barred from the daily policing of Americans. But it can be used to quell rebellions

The 1878 Posse Comitatus Act mostly prohibits active-duty military troops from carrying out law enforcement duties inside the United States.

The idea behind the law is that any president -- as commander in chief of U.S. forces -- shouldn't be allowed to use federal military might against its own citizens.

But it's a different law that was passed earlier that century that's caught the attention of many Trump supporters.

First enacted in 1807, the Insurrection Act says the president can call on a militia or the U.S. armed forces if there's been "any insurrection, domestic violence, unlawful combination or conspiracy" in a state that "opposes or obstructs the execution of the laws of the United States or impedes the course of justice under those laws."

The Insurrection Act has been used dozens of times throughout history, but not by Trump

According to the Brennan Center for Justice, the law has been invoked dozens of times throughout history, including by Abraham Lincoln during the Civil War and by Lyndon B. Johnson to quell rioting after the assassination of Martin Luther King Jr.

In 1957, President Dwight D. Eisenhower used the law to deploy members of the Army's 101st Airborne Division to escort nine Black students into Little Rock Central High School, after the Arkansas governor used the state's National Guard to prevent the students from entering the school.

More recently, the law was invoked by President George H.W. Bush during the 1992 riots in Los Angeles that followed the trial acquittal of police officers in the Rodney King case. The law was also under consideration in 2005 following Hurricane Katrina, but was not used.

In the days leading up to the Jan. 6 riot, some Trump supporters wanted the president to invoke the Insurrection Act as a justification for far-right militia groups to storm the Capitol and to keep Trump in power despite losing the election.

Trump falsely claimed he won the election, but never invoked the Insurrection Act while in office.

Experts warn the law is dangerously vague

Legal experts have proposed reforms to the Insurrection Act, including one proposal earlier this year by the American Law Institute.

"There is agreement on both sides of the aisle that the Insurrection Act gives any president too much unchecked power," Jack Goldsmith, a Harvard law professor and former assistant attorney general in the Bush administration, said last April.

It's unlikely, though, that such a sharply divided Congress would take up the issue any time soon.

There's another law, too, that Trump could try to rely on when it comes to handling illegal immigration -- the 1798 Alien Enemies Act, which allows the president to deport any noncitizen from a country that the U.S. is at war with.

In his interview with Time magazine this year, Trump didn't cite a legal justification when he said he'd use the National Guard to conduct mass deportations and create detention camps for people living illegally inside the U.S.

In the end, whether any of Trump's proposals are legal would likely be determined by the courts, including federal judges he appointed.