Originally Posted by kane

While there is no real checks and balances other than his advisers suggesting he not launch there are at least a few people between the POTUS and the actual missile launching. For example, on land-based missiles it takes a team of two people with keys to launch it If one refuses, that missile won't launch.

There are stop gaps put in place so the POTUS can't just wake up one morning, be pissed off, and launch a couple of nukes at a target. He has the power to do it, but there are a lot of people who could prevent it.