Insurrection Act...

I'll just leave this morsel here. Make of it what you will. 

10 USC Ch. 13: INSURRECTION

From Title 10—ARMED FORCESSubtitle A—General Military LawPART I—ORGANIZATION AND GENERAL MILITARY POWERS

§253. Interference with State and Federal law

The President, by using the militia or the armed forces, or both, or by any other means, shall take such measures as he considers necessary to suppress, in a State, any insurrection, domestic violence, unlawful combination, or conspiracy, if it—

(1) so hinders the execution of the laws of that State, and of the United States within the State, that any part or class of its people is deprived of a right, privilege, immunity, or protection named in the Constitution and secured by law, and the constituted authorities of that State are unable, fail, or refuse to protect that right, privilege, or immunity, or to give that protection; or

(2) opposes or obstructs the execution of the laws of the United States or impedes the course of justice under those laws.

There's more at US.gov