There's nothing unusual about a mayor being trailed by a bodyguard -- unless, that is, he needs to be protected from assassins working on behalf of the president of his own country. But then, Leopoldo Lopez of Caracas is not your usual mayor and Hugo Chavez of Venezuela is not your usual president. Lopez -- 36, educated at Harvard's Kennedy School of Public Policy, and mayor of Chacao, one of five municipalities within Caracas -- has emerged as one of the most visible challengers to the increasingly authoritarian Chavez regime. That's a dangerous undertaking. Lopez recounts three assassination attempts --...