The Military should not act as Police
It is extremely dangerous, and unconstitutional, to use the military for policing. The military and the police have opposite functions. The purpose of the military is to kill people and break things. The role of police is to serve and protect. To use the military as police will inevitably result in more people being killed and more things being broken. At the other extreme, we see police forces around the country being “militarized” through use of weapons such as tanks and heavy firearms and military vehicles. This will cause the police to view protesters as the enemy, rather than as people who they should protect and serve.
roymilleraz 
If the social order breaks down to such an extent that civilian law enforcement is overwhelmed and clearly incapable of establishing peace and security of the nation’s citizens, then a chief executive would be derelict to not temporarily deploy military forces to protect life and limb of innocent people unable to defend themselves and their homes. Apparently there is federal law providing for just such a contingency, and I for one believe in very limited circumstances the president should exercise that authority.
The governors have the ability to call out the National Guard.
What I envision are situations where the National Guard becomes overwhelmed by the wide-spread extent of civil disorder and themselves need backup. We have a number of recent historical examples in which presidents have federalized Guard troops or as did President Eisenhower deploy active duty troops (Little Rock High School desegregation) to maintain order and protect lives. The presence of elements of the 82nd or 101st Airborne Divisions as a last resort (before we armed citizen militias have to join in a civil war) shouldn’t be such a big negative concern which some people have about an infrequent limited use of active duty soldiers to restore the peace to communities aflame from wide-spread rioting. I am far more concerned with retired flag officers engaging in what is tantamount to an attempted coup against a duly-elected president to try to maintain the control which the Deep State has over this country.