Congress is authorized "To provide for calling forth the militia to execute the laws of the Union, suppress insurrections, and repel invasions," and "To provide for organizing, arming, and disciplining the militia, and for governing such part of them as may be employed in the service of the United States, reserving to the states respectively the appointment of the officers, and the authority of training the militia according to the discipline prescribed by Congress " (Const Art. I, § 8, ¶¶ 15, 16). It is evident that the militia here referred to is the militia of each state, and that when thus called out for federal purposes, the militia of a state becomes a military force of the federal government. The method of calling out the militia is prescribed by federal statute, and the command over them, as over other military forces of the United States, is vested in the president (Art. II, § 2). His exercise of this power will be considered in the chapter relating to his war powers. (See below, § 131.)