The Martial Law Statute
The current text of Section 333 of Title 10 of the United States Code:
Interference with State and Federal lawThe 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.In any situation covered by clause (1), the State shall be considered to have denied the equal protection of the laws secured by the Constitution.
This purports to give the President considerable discretion to impose martial law, but it is better, as far as power placed with the president, than the 2006 version of the law, which was entitled, "Major public emergencies; interference with State and Federal law":
(a) Use of Armed Forces in Major Public Emergencies-(1) The President may employ the armed forces, including the National Guard in Federal service, to–(A) restore public order and enforce the laws of the United States when, as a result of a natural disaster, epidemic, or other serious public health emergency, terrorist attack or incident, or other condition in any State or possession of the United States, the President determines that–(i) domestic violence has occurred to such an extent that the constituted authorities of the State or possession are incapable of maintaining public order; and(ii) such violence results in a condition described in paragraph (2); or(B) suppress, in a State, any insurrection, domestic violence, unlawful combination, or conspiracy if such insurrection, violation, combination, or conspiracy results in a condition described in paragraph (2).(2) A condition described in this paragraph is a condition that–(A) so hinders the execution of the laws of a State or possession, as applicable, and of the United States within that State or possession, 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 or possession are unable, fail, or refuse to protect that right, privilege, or immunity, or to give that protection; or(B) opposes or obstructs the execution of the laws of the United States or impedes the course of justice under those laws.(3) In any situation covered by paragraph (1)(B), the State shall be considered to have denied the equal protection of the laws secured by the Constitution.(b) Notice to Congress- The President shall notify Congress of the determination to exercise the authority in subsection (a)(1)(A) as soon as practicable after the determination and every 14 days thereafter during the duration of the exercise of that authority.
Interestingly, the 2008 version of Section 333 is the same as the 1956 version, which suggests to me that someone in Congress may actually be looking out for our interests... unless the powers removed from section 333 in 2008 wound up in some other statute.