The proposition at the heart of The Kennedy Assassination: 24 Hours After, Steven M. Gillon’s examination of the immediate aftermath of President John F. Kennedy’s death, in Dallas, is that Lyndon B. Johnson’s actions during his first day in office foreshadowed the high and low points of his presidency. So when LBJ hunkers down through the night with his advisers, it presages the promise of his Great Society, and when he is cowed by Kennedy’s fanatically loyal staff and family, it supposedly foretells his failures in dealing with Vietnam and the race riots on the home front. The idea is intriguing, considering the chaos and trauma that tested Johnson in those 24 hours, but the incidents offered as proof (a farcical misunderstanding about whether Jackie or LBJ should use Air Force One, LBJ’s insistence on being sworn into office as soon as possible) are not numerous or consequential enough to support the weighty conclusions being made. The details and personal memories of the Kennedy assassination have been so thoroughly and publicly dissected that Gillon’s book cannot help but appear as a puffed-up rehashing of familiar anecdotes, with a central thesis that could have been distilled into a thoughtful, sharply drawn magazine feature. Basic Books, $25.95