Recent congressionally passed law, now repealed, may have explicitly given this authority to the President. HR5122 also known as the John Warner Defense Authorization Act was signed by the president on Oct 17, 2006 John Warner National Defense Authorization Act for Fiscal Year 2007. Section 1076 Text of Hr5122 is titled "Use of the Armed Forces in major public emergencies". Removing the legalese from the text, and combining multiple sentences, it provides that: The President may employ the armed forces to restore public order in any State of the United States the President determines hinders the execution of laws or deprives people of a right, privilege, immunity, or protection named in the Constitution and secured by law or opposes or obstructs the execution of the laws of the United States or impedes the course of justice under those laws. The actual text is on page 322-323 of the legislation. As of 2008, these changes were repealed, changing the text of the law back to the original 1807 wording.
Every single one of the Founding Fathers, from those first legislators, to those men who were eagerly waiting in bars and taverns for news, are rolling in their graves.
Like somebody on here once said, the Founding Fathers rolling in their graves is an incredible source of untapped energy.