There he was, the 27-year-old John Kerry, hair spilling down over his eyes, Kennedyesque a's (as in "cahn't imagine") rolling off his tongue, and lanky legs seeking room on the cramped talk show set. C-SPAN was rebroadcasting an episode of "The Dick Cavett Show" from 1971. Opposing Kerry was a hard-charging, highly intelligent Vietnam veteran named John O'Neill, who gave the future senator no quarter. It was just two months after Kerry's pyrotechnic performance before the Senate Foreign Relations committee, in which he had famously declared that American soldiers in Vietnam had "personally raped, cut off ears, cut off heads,...