JP 3-28, page 29

Overview I-7 and DOD conducts DSCA operations in support of another primary agency supporting a state, local, territorial, or tribal response. DOD works with DHS and other USG departments and agencies to accomplish these missions. 4. Fundamentals of Response a. State and local officials are responsible for preparing for and coordinating the provision of assistance to their populace for domestic emergencies and disasters. Governors have the authority to deploy and employ NG forces under their control in response to domestic incidents. NG forces in most situations will be employed under their control prior to requesting federal assistance; however, a governor may request federal assistance in parallel. b. The USG maintains a wide array of capabilities and resources that can be made available upon request of the governor of a state or local civil authorities for immediate response or under mutual aid agreements. When an incident occurs that exceeds or is anticipated to exceed state, local, or tribal resources, both neighboring states and the USG may provide resources and capabilities to support the response (see Figure I-2). Interstate mutual aid and assistance is provided through prearranged agreements such as the emergency management assistance compact (EMAC). The EMAC is a federal statute, nationally accepted by all states, to allow interstate mutual-aid agreement that enables states to share resources and certifications during times of disaster. For incidents involving Figure I-2. Layers of Redundant Capabilities When a situation is beyond the capability of an affected state or territory, the governor may request federal assistance from the President. Federal State, Territory, and Tribal Nation County City Request from Governor Capabilities Layers of Redundant Capabilities    Department of Homeland Security (Federal Emergency Management Agency) Department of Defense Other United States Government Departments and Agencies    State Emergency Management State Troopers National Guard     County Emergency Management County Hospital Fire and Rescue County Sheriff   Local Fire Local Police