what does "That one existed must be traced to men's minds, not to the law of the land"mean?
In 1963, when the warning time for nuclear missiles from the Soviet Union had been reduced to less than a quarter:hour, any Presidential hiatus was intolerable. There ought to have been no interregnum. That one existed must be traced to men's minds, not to the law of the land. The most brutal murder in American history seemed to be the paramount fact that Friday afternoon. It overwhelmed everyone, and the stunned nation demanded to know the identity of the assassin. No one at the press con¬ference thought to ask the identity of the man who, at that very moment, occupied the mightiest office in the world. Yet there was an answer. The Presidency, like an immortal heart, never stops. America had a new Chief Executive. His name was Lyndon Baines Johnson, and although even he did not realize it, he had been in power for over an hour.