In an episode first reported in 2017, we bring you a look up and down the US nuclear chain of command to find out who gets to authorize their use and who can stand in the way of Armageddon. 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? In...