In the film, National Treasure: Book of Secrets, Benjamin Gates must locate the Presidential Book of Secrets. The only person who knows the location of the book is the President of the United States. Benjamin decides to attend a birthday party for the President at Mount Vernon. Benjamin then intrigues the President with the history of Mount Vernon and lures him to an underground tunnel to get him alone to ask about the location of the book. He has the President alone and trapped in a room. Ben explains everything to him and the President helps him and gives him the information that he needed:
President: The following conversation never happened...The book exists.
Gates: Where is it?
President: Where else do you keep a book? The Library of Congress.
The President then goes on to tell Benjamin that he can't tell anyone why Benjamin held him against his will:
President: Gates...Two Hundred people will know that you held me against my will. I can't tell them why. Unless you find what you're looking for, you will be charged with kidnapping the President.
The FBI is then chasing after Benjamin and his associates throughout the remainder of the film. After Benjamin found what he was looking for, he is brought into custody by the FBI. The President is waiting for Benjamin when he arrives and tells everyone that he wasn't kidnapped and that Benjamin saved his life:
President: As I recall, we were exploring a hidden tunnel, and a door closed accidentally and this man saved my life.
Why didn't the President just tell everyone this story to begin with? What was the purpose of the President saying that he was kidnapped? Is there some out-of-universe explanation that filmmakers chose to incorporate into the film regarding the kidnapping of the President of the United States?