How could President Trump use the National Guard in Chicago?

CHICAGO (WLS) -- The National Guard has historically been used to serve the U.S.

The modern-day National Guard was created under the Militia Act of 1903. The Guard is trained for war, but serves stateside, as well.

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But, as current and retired guardsmen say, they don't serve in the capacity of fighting crime.

They have been seen keeping an eye on the National Mall in Washington, D.C. and guarding federal buildings in Los Angeles. Despite President Donald Trump's intentions for the use of the National Guard, under law, there are limits on how a president can use the Guard stateside.

"They have a dual role. They support the state governors in their respective states, and then they also support the country in a federal matter, if needed," said retired Maj. Gen. David Harris, adjutant general for the Illinois National Guard.

If a governor does not request the Guard, the president can federalize them under Title 10 of the U.S. code. Harris says a president can deploy the National Guard for several reasons, but none amount to helping reduce local crime.

"He can call them to quell a civil disturbance, to quell a rebellion or to enforce federal laws. As an example, what President Johnson did in forcing Gov. Wallace in Alabama to call the Guard out to enforce the civil rights laws that were passed in mid-60s," Harris said.

Presidents have also used the National Guard for disaster relief.

"They were mobilized during Hurricane Katrina, you know, because they have capability that ordinary police don't, you know, transport, logistics, supply. You know, they can move a lot of stuff, a lot of people, very quickly," said Professor Tom Mockaitis, DePaul University military historian.

The National Guard is part of the national military force. They are trained just like active duty personnel to fight in wars. They carry weapons of war. If called to Illinois to curb crime, the Guard cannot be dispatched by 911 to crime scenes, and federal communication equipment cannot interact with local first responders.

"It is problematic if radio sets are not designed to communicate with police, fire and emergency responders," Mockaitis said.

The Guard does not have arresting powers unless they are federalized under the Insurrection Act. Because the use is limited for the president, military experts say if troops are deployed to Chicago, they will likely be used to guard federal buildings.

While President Trump has seemed to back off a bit from his plan to send the National Guard to Chicago, the governor or the mayor have yet to receive any type of communication from the Trump administration about a plan.