The group has hired Jessica Mackler, who most recently ran former Rep. Shelley Berkley's (D-Nev.) Senate campaign, and Eddie Vale, who has been running communications for the AFL-CIO's super-PAC. Both will be vice presidents at the organization, which specializes in opposition research on GOP candidates and helped damage a number of Republicans, including Mitt Romney.

"As we prepare to build on the success of the last election cycle, Jessica and Eddie will be valuable additions to American Bridge and bring years of experience right in line with our core mission," American Bridge President Rod Mollineau said. "They will further strengthen a rock-solid senior staff and organization that I couldn't be prouder of."

The group had a strong 2012 cycle, and many Democrats have credited it for leading the way in damaging GOP candidates. Republicans are hoping to counter this cycle with America Rising, a new group headed by former Romney campaign manager Matt Rhoades, focused on opposition research.