Three hundred nuclear missiles are screaming towards the US. This is likely a pre-emptive strike by Russia to destroy all land-based intercontinental ballistic missile silos in the country. Anti-missile defences cannot knock out many of the incoming rockets, meaning 2mn Americans will die.
Having been sworn in as US president a few minutes previously, I am sitting in the Oval Office watching TV reports of escalating fighting in Europe. A secret service agent bursts into the room and tells me to leave immediately. I take the lift down to the White House crisis centre known as the Situation Room, where I am joined by my top national security officials, who brief me on the incoming attack. I have 15 minutes to respond. As the clock ticks down, I am presented with three options, all of which involve retaliatory strikes against Russia, projected to kill between 5mn and 45mn people. What do I do?
