The book explains: ‘He firmly pushed the stock into his shoulder, ready to fire. He’d expected the footsteps to retreat with the loud sound of the gun activating, but they kept coming closer. Blaine’s heart pounded, his finger firmly on the trigger. Let me see your face, you bastard.

‘The next instant, there was a face to go with the footsteps.

‘The new President of the United States, Lyndon Baines Johnson, had just rounded the corner, and Blaine had the gun pointed directly at the man’s chest. In the blackness of the night, Johnson’s face went completely white.

‘A split second later, Blaine would have pulled the trigger…

‘Blaine struggled to regain his composure as the reality of what had just happened washed over him. Fourteen hours after losing a president, the nation had come chillingly close to losing another one.’