The John Warner National Defense Authorization Act of 2007, signed by President Bush on October 17, 2006, “authorizes the president to determine, at his sole discretion, that the authorities of a given state or possession are ‘unable, fail, or refuse’ to address a public emergency. In that event, he is authorized to ’employ the Armed Forces, including the National Guard in Federal Service,’ to ‘restore public order.’ This latter clause empowers the president to take command of state National Guard units without the consent of the governors.”
– Eugene Jarecki, The American Way of War, Page 245