How would a US President launch a nuclear attack?

A few hours before his inauguration, Donald Trump, as President of the United States and Commander-in-Chief, was given a small plastic card. This gives him the authority to unleash thousands of nuclear warheads. What are the steps that would need to be taken to launch a nuclear strike? Bruce Blair, a former nuclear launch missile officer, and presenter Ruth Alexander outline the process.

(Photo: A Trident Ii, Or D-5 Missile, Is Launched From An Ohio-Class Submarine. Credit: Getty Images)