The president may seem like a very authoritative figure, and after all, he's part of our military and the executive branch of government. He or she is responsible for carrying out the law - the whole branch is, actually. The United States Constitution doesn't grant to much rights toward the President in times of national emergency or a crisis. Although - no president should ever have to go that far in terms of a national crisis. The president must get approval from Congress to initiate any procedures during a time of national crisis. This includes war on another country and a potential target. That's the main reason.
