As of this March, the federal budget spending is in three categories: Mandatory, which is at $2.841 trillion; Discretionary at $1.426 trillion; and interest on

As of this March, the federal budget spending is in three categories: Mandatory, which is at $2.841 trillion; Discretionary at $1.426 trillion; and interest on the national debt, $479 billion. Of those three, the DOD is about half of the Discretionary category, so totaling about 15% of the budget overall. In other words, the only budget item that the Constitution explicitly calls for is considered discretionary, and is less than 20% of the overall spend.