The respective state National Guards are authorized by the Constitution of the United States. As originally drafted, the Constitution recognized the existing state militias, and gave them vital roles to fill: "to execute the Laws of the Union, suppress Insurrections and repel Invasion." (Article I, Section 8, Clause 15). The Constitution distinguished "militias," which were state entities, from "Troops", which were unlawful for states to maintain without Congressional approval. (Article I, Section 10, Clause 3). Under current law, the respective state National Guards and the State Defense Forces are authorized by Congress to the states and are referred to as "troops." 32 U.S.C. § 109.
Yet the President of the United States is the commander-in-chief of the state militias "when called into the actual Service of the United States." (Article II, Section 2).
The traditional state militias were redefined and recreated as the "organized militia"—the National Guard, via the Militia Act of 1903. They were now subject to an increasing amount of federal control, including having arms and accouterments supplied by the central government, federal funding, and numerous closer ties to the Regular Army. - http://en.wikipedia.org/wiki/National_Guard_of_the_United_States#Constitutional_basis
But..... the NG can be deputized as law enforcement and be under the direct control of the governor.
The military hats come off and Law enforcement hats go on