"To make rules for the government and regulation of the land and naval forces"

John McCain says it’s unconstitutional for Congress to make rules about the length of service of military personnel in the Iraqi combat zone. John McCain is an idiot. He should read Section 8 of Article 2 of the Constitution before he spouts off nonsense.
The Constitution says Congress shall have the power:

To declare war, grant letters of marque and reprisal, and make rules concerning captures on land and water;
To raise and support armies, but no appropriation of money to that use shall be for a longer term than two years;
To provide and maintain a navy;
To make rules for the government and regulation of the land and naval forces;
To provide for calling forth the militia to execute the laws of the union, suppress insurrections and repel invasions;
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;