The President Is the Commander-in-Chief
As is well-known, the President is the Commander-in-Chief of the armed forces of the United States. The reason is that the Constitutional Convention was very wary of the possibility that we might wind up with a Constitution in name only. For example, the Roman Emperors were, at first, not dictators. (Roman dictators were term limited anyway.) They were instead the Commander-in Chief of the armed forces. (ObSF: Francis X. MacHinery in They Shall Have Stars by James Blish.) The Constitutional Convention was trying to avoid that by ensuring that the President is the Commander-in-Chief instead of someone outside the Constitution. In other words, the armed forces must commanded by someone who can be defeated for re-election, can be impeached if necessary, is term-limited, and whose budget can be cut. It does not mean he has absolute power.