First, a few US Constitution and federal law cites:
The Second Amendment: A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
Article 1 Section 10 of the Constitution: "No State shall, without the Consent of Congress...engage in War, unless invaded, or in such imminent Danger as will not admit of delay."
Under 32 USC 109, the federal government recognizes state defense forces, aka State Guards, State Military Reserves, State Militias. This force may not be called, ordered, or drafted into US armed forces, e.g. the National Guard.
The Militia Act of 1903 created two classes of militias: 1) organized, i.e. the National Guard, and 2) unorganized, i.e. every able-bodied man 17-45 who is not a member of the National Guard or reserve.
And this from the Arizona Constitution:Chapter 1, Article 2, Revised Statute 26-124:
A. When the governor proclaims an emergency, and, upon advice of the adjutant general, determines that the national guard does not have sufficient troops to meet the emergency, the governor may authorize the adjutant general to accept for service from the unorganized militia a specified number of volunteers.
B. If the governor deems an emergency of a nature that all or a large portion of the unorganized militia should be called into service of the state, s/he shall by proclamation order all members of the unorganized militia to enroll with the county recorder of the county in which they reside...The persons called into service shall be determined by lot in accordance with a plan devised by the governor and implemented by him/her...
C. Upon mobilization for state purposes members of the unorganized militia shall be organized under the command of the officer the governor designates into units comparable to units of the national guard.
Note: while the Posse Comitatus Act limits the power of the federal government to use the militia for law enforcement, it does not prevent a state governor's calling up the National Guard OR the state militia to respond to domestic emergencies and disasters.
Recent Arizona developments:
My understanding is that a volunteer state military force (aka Homeland Security Force) has yet to be formally mustered which the state could call upon in the event the state's reliance upon the National Guard for homeland security purposes is somehow pre-empted by the federal government or if the National Guard is otherwise unavailable to the state.
Whether what is happening in Arizona constitutes an invasion or a domestic emergency/disaster, it seems abundantly clear to me that the Governor is constitutionally empowered to unilaterally call up the Militia in order to protect the citizens of Arizona whose security is her constitutional responsibility.So, why hasn't Governor Brewer called up the militia? First, because unlike 22 other states which have formally established State Militias (apart from the National Guard), Arizona does not. Also, her calling up the Militia might well be viewed by many Americans as an over-reaction and, of course, there is the political risk should the militiamen be improperly trained. Or perhaps she's just biding her time until it becomes crystal clear to all that Obama has no intention whatsoever of honoring his constitutional responsibility--that being to properly protect the border--and that she has, therefore, no other recourse if she is to safeguard the citizens of Arizona.
My guess is that if the situation further deteriorates, the Governor cannot in good conscience or in good faith avoid a call-up of the State Militia. And I suspect her action in this regard would be overwhelmingly supported by most Arizonans and Americans everywhere. At least it should be.
My personal belief is that all States--and let Arizona lead the way--must begin, in earnest, to properly prepare themselves to credibly resist both federal overreach and federal dereliction at every turn. Because we live in increasingly perilous and uncertain political times, all states should re-commit themselves to properly asserting their rightful sovereignty as provided by the founders and the Tenth Amendment. If liberty and the Republic are to survive the relentless Progressive onslaught, there is simply no other reasonable option.