If President Trump does use the military to quell protests, he’ll likely rely on the same law used to aid the Civil Rights movement

After a week of both peaceful protests and violent chaos in the wake of George Floyd’s death, President Donald Trump announced, “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.”

Is Trump’s warning just bluster? Does the president have the authority to send the military into American cities?

The answer to this question involves a web of legal provisions that help define the president’s constitutional roles as commander in chief and chief executive of the country and that simultaneously try to balance presidential power with the power of state leaders.

Tracing back to the Magna Carta, the British charter of liberty signed in 1215, there is a longstanding tradition against military involvement in civilian affairs.

However, the U.S. Constitution guarantees that the national government will protect the states in times of violence and permits Congress to enact laws that enable the military to aid in carrying out the law.

Almost immediately after the Constitution’s enactment in 1787, Congress passed a law that allowed the president to use the military to respond to a series of citizen rebellions.

Troops serving as what’s called “posse comitatus,” which translates roughly to “attendants with the capacity to act,” could be called to suppress insurrections and help carry out federal laws.