One of the central principles of a democratic country is that the military is not used against civilians. "But those civilians are criminals" is the excuse that every president who wants to use the military internally will make. Civilians have rights, and if they're suspected of a crime, that's a matter for the police and the courts, not for the military. If you give the executive the power to send the military onto the streets, that is an extremely dangerous concentration of power in one person's hands.
The use of the military against civilians was one of the main grievances that led to the American Revolution (most notably, the British government sending the regular army into Boston to "restore order"). Many of the founders of the US were opposed to the idea of any standing army at all in peacetime, because of its potential use against the citizens of the country.
The military should never, ever be used to "police" their civilians. You could be forced to apprehend your relative. When the military attacks the civilian population then civil war is inevitable.
The use of the military against civilians was one of the main grievances that led to the American Revolution (most notably, the British government sending the regular army into Boston to "restore order"). Many of the founders of the US were opposed to the idea of any standing army at all in peacetime, because of its potential use against the citizens of the country.