Sen. John Kerry's bid to become commander in chief of wartime America has opened old wounds among some former Vietnam-era prisoners of war who bristle over the Massachusetts Democrat's anti-war activism. His activities and statements, pushed out of sight by a campaign that spotlights Mr. Kerry's service in Vietnam, were used by the POWs' North Vietnamese captors to sap the morale of prisoners and U.S. troops still in the field in South Vietnam, say former POWs. "They were always talking about [anti-war demonstrations], and they picked right up on Kerry's throwaway line, 'Don't be the last man to die in...