This is pretty sad when active duty military units are now on alert to respond to violence because local and state authorities are unwilling to stop it:
As unrest spread across dozens of American cities on Friday, the Pentagon took the rare step of ordering the Army to put several active-duty U.S. military police units on the ready to deploy to Minneapolis, where the police killing of George Floyd sparked the widespread protests.
Soldiers from Fort Bragg in North Carolina and Fort Drum in New York have been ordered to be ready to deploy within four hours if called, according to three people with direct knowledge of the orders. Soldiers in Fort Carson, in Colorado, and Fort Riley in Kansas have been told to be ready within 24 hours. The people did not want their names used because they were not authorized to discuss the preparations.
Stars & Stripes
You can read more at the link, but active duty servicemembers do not have policing powers due to the Posse Comitatus Act, the National Guard does though. This is why the Guard is called in to deal with situations like this.
If active duty units are sent, according to the article they will be deployed using the Insurrection Act of 1807. If you click the link you can read more about the act which essentially allows the government to deploy active duty troops if the Posse Comitatus Act fails to stop lawlessness, insurrections, or rebellions. I would be very surprised if these escalated to the point of needing active duty troops.
