According to Wikipedia the authority comes from H.R. 5122 signed into law by G.W. Bush in 2006, which “gave the president the power to declare martial law and t

According to Wikipedia the authority comes from H.R. 5122 signed into law by G.W. Bush in 2006, which “gave the president the power to declare martial law and to take command of the National Guard units of each state without the consent of state governors.”