The fight for Arizona's second district was one of the closest in the nation last cycle, with Barber defeating McSally by just over 2,000 votes.

And he remains one of Republicans' top targets in 2014. His district was redrawn to become slightly more Democratic, but Republican Mitt Romney won it in 2012.

Barber, who previously worked as a staffer for former Rep. Gabrielle Giffords (D), was first elected to the district in a special election to replace his boss following her resignation due to injuries incurred at a shooting in Tucson, Ariz.

McSally, an Air Force veteran, ran a race that many observers considered surprisingly adept, and Republicans believe with an earlier start and the enthusiastic backing of the national party she'll be able to topple Barber in a rematch.