Fascinating Radiolab podcast today: "Nukes"
http://www.radiolab.org/story/nukes/
"President Richard Nixon once boasted that at any moment he could pick up a telephone and - in 20 minutes - kill 60 million people. Such is the power of the US President over the nation’s nuclear arsenal. But what if you were the military officer on the receiving end of that phone call? Could you refuse the order? This episode, we profile one Air Force Major who asked that question back in the 1970s and learn how the very act of asking it was so dangerous it derailed his career."
Short version: The missileers - the specialists who would launch intercontinental nuclear missiles - are subject to a strict system of checks and balances. For example, they have to confirm their orders out loud to one another, then they each have to turn a key simultaneously to launch the missile. They both carry weapons, partly to protect themselves from one another in case the other specialist goes rogue.
However, at the top of the chain of command where the orders originate, there are no checks and balances. The decision to launch an ICBM is entirely up to POTUS with no obligation to consult anyone else. One reason is that people believe any nukes launched toward the U.S. would target land-based missile sites so if they don't act within 6 or 7 minutes, they will lose their chance to retaliate.
With all due respect to my Republican friends, this is terrifying given the impulsiveness of the current White House occupant - plus a few other characteristics.