Charleston, W.Va. -- Thomas Esposito's campaign for the Legislature seemed to be following the usual pattern. The longtime Democratic mayor issued press releases, raised money and bought newspaper ads. Signs bearing his name popped up in yards around rural Logan County. But less than a month before the May 2004 primary election, Esposito dropped out, saying he had to withdraw because of his ailing mother-in-law. The real reason surfaced only later: The FBI had planted Esposito among the field of candidates to help find evidence of vote-buying in southern West Virginia. Federal prosecutors say the gambit worked. They allege Esposito...