What is the main conflict in Profiles in Courage by John F. Kennedy?

Throughout his youth, John F. Kennedy suffered numerous ailments. When he endured two near-fatal spine operations in 1954, he decided to put his recovery period to good use. He and his aides (he was a U.S. Senator at the time) began a book profiling American politicians he admired for their courage and individualism in the face of party and constituent pressures. Kennedy was particularly struck by how these nine men were willing to risk their political careers to maintain the integrity of their personal value systems and their love of country. This book, of course, became Profiles in Courage, which was published in 1956.