[Sailor Steve]

Thanks for posting the link, Markus. I think you'll find the most important description and point is here.

g. Federal military commanders, Heads of DoD Components, and/or responsible DoD civilian officials (hereafter referred to collectively as "DoD officials") have IMMEDIATE RESPONSE AUTHORITY as described in this Directive. In response to a request for assistance from a civil authority, under imminently serious conditions and if time does not permit approval from higher authority, DoD officials may provide an immediate response by temporarily employing the resources under their control, subject to any supplemental direction provided by higher headquarters, to save lives, prevent human suffering, or mitigate great property damage within the United States. Immediate response authority does not permit actions that would subject civilians to the use of military power that is regulatory, prescriptive, proscriptive, or compulsory.

According to that clause the document gives the Department Of Defense the authority to respond to requests for help from state and local authorities to help with situations that threaten lives or property. The last sentence specifically forbids the military from using that article to do anything against US citizens.