As World War II was ending and the cold war was just beginning, a twenty-eight-year-old naval hero, decommissioned before war's end because of his crippling injuries, traveled through a devastated Europe. During that trip, John F. Kennedy kept a diary, never before published and until now unknown - even to Kennedy scholars. As the diary makes clear, that European trip was a turning point in the future President's life.

The scion of one of America's wealthiest families, Jack Kennedy had grown up in the shadow of an adored older brother destined for greatness. For himself, Jack had intended a quiet career as a college professor or perhaps as an author.

But when Joe Kennedy, Jr. was killed in the skies over the English Channel, the expectations of his family and the mantle of leadership passed on to JFK. Would he accept them? That was the question that confronted Kennedy as he traveled in the company of cabinet secretaries and generals, future presidents and prime ministers, toured a humbled Germany, and faced for the first time the power of post-war Russia and the perfidy and bloody-mindedness of Communists in power.

It was on this trip, the diary shows, that Kennedy first confronted the "long twilight struggle" for the preservation of Western freedom that would define his Presidency. In these few months an agenda for a Presidency began to be forged. For as the closing pages of the diary make clear, it was at this time that the challenge was accepted, the mantle taken up, and Kennedy began laying plans for his first run for Congress, the first step in his journey to the White House.

Prelude to Leadership offers, as Hugh Sidey says in his Introduction, an "intriguing new trove" of insight into the mind of a future president preparing himself for a "still distant challenge." It reveals a man who, not yet thirty, understood not only that a new world drama was taking shape, but that he was destined to play a great role in it.