ATLANTA — Democrat Michelle Nunn and Republican David Perdue share the title of CEO but are trying to make the case their experiences couldn’t be more different as they campaign for Georgia’s open Senate seat. Both candidates are political newcomers who see their business backgrounds as key to wooing independent voters in a race that has garnered national attention as Republicans seek control of the Senate. The candidates also see an opportunity in attacking their opponent’s business record as they look to the general election.