NEWNAN — Georgia Democrat Michelle Nunn has spent the past month hammering away at Republican David Perdue’s career as a business executive, making his role in outsourcing jobs a hallmark of her campaign for U.S. Senate. With fewer than two weeks to go, Republicans think they’ve weathered the storm and remain bullish on their chances to pick up the six seats they need to regain a Senate majority. But Nunn could yet complicate the GOP’s path by squeezing out a victory — or at least force a runoff that would leave the midterm congressional elections unsettled until January.