With reference to the protection of the state governments and interference in state affairs, the government of the United States has no other authority than to "guarantee to every state in this Union a republican form of government," and "protect each of them against invasion; and on application of the legislature, or of the executive (when the legislature cannot be convened), against domestic violence" (Const. Art. IV, § 4). The duty to guarantee a republican form of government does not, perhaps, rest especially on the president; but, as the head of the military and naval forces of the United States, it is within the scope of his duty to give protection against invasion and domestic violence, and Congress by act of 1795 provided for the exercise by him of this function. He may call out the militia of other states for this purpose, and, as the final and conclusive authority, must determine whether an emergency exists requiring the exercise of his authority. (See Martin v. Mott.) It may be necessary for him to determine whether there is a state government, and, as between conflicting claims of different persons or bodies, who is the lawful executive of the state and which is the lawful legislative body thereof. These are among the political powers of the federal government, and such powers are necessarily in the executive rather than in the legislative or judicial department. Each department, however, can determine questions of this character, necessarily arising before it in the discharge of its duties. Thus, the Senate of the United States may have to determine which of two senators elected by rival state legislatures is entitled to a seat as senator from the state; and the judicial department may find it necessary, in a suit brought by a state, to determine whether the government purporting to act for the state in bringing such suit is the lawfully authorized government of the state. But so far as the president is called upon, in the discharge of his duties, to determine the legality or illegality of a state government, his action cannot be overridden or reviewed by either of the other departments of the federal government. It is to be noticed that there is a distinction between the power of the president to protect a state against invasion and domestic violence and his power to enforce the laws of the United States. (See above, § 122.) In the one case he acts only upon the call of the state government, in the other he acts under his authority as chief executive of the United States to see that its operations are not interfered with or hindered, and with reference to the discharge of his duties in this respect the request of the state government is wholly immaterial and its protests would be unavailing. The authority of the president in enforcing the laws of the United States cannot be made to depend upon state action.