This time, however, Barber trails McSally by just over 400 votes. Thousands of early ballots and provisional ballots have yet to be counted, and Barber's campaign has expressed confidence that he'll pull it out in the end.
"We are cautiously optimistic about what the early ballots that were walked in will look like," Jessica Floyd, Barber's campaign manager, told the Arizona Daily Star.
Barber, Giffords's former aide who was hand-picked to succeed her in a special election after she resigned from Congress to recover from a 2011 shooting, was the early favorite in the race.
But the district is nearly equal parts Democratic, Republican and independent in voter registration, and McSally ran a strong campaign, making a concerted effort to appeal to veterans and women.
Barber told The Associated Press that he'll support McSally's election if the current state of the race holds.
“I’m perfectly at ease and at peace with the voters’ decision about who they send to Congress,” he said. “And if it’s not me, then I wish my opponent, if she’s our new member, every success because we have to get the job done."
Barber, along with Giffords and her husband Mike Kelly, spent much of Thursday morning at the court hearing for Jared Loughner, the gunman in the shooting that injured Giffords. Barber and Kelly are scheduled to speak.