Wednesday's presidential debate is one of those Big Moments—and not just for the candidates competing. The army of opposition researchers at American Bridge 21st Century, a Washington-based liberal super PAC, has prepared for more than a year for nights like this. Dozens of Democratic worker bees have combed through thousands of hours of video of Republican nominee Mitt Romney. And they plan to unload the worst of what they've dug up in the run-up to the debate.

The onslaught began last weekend, when American Bridge launched the first stage of its Romney takedown with a Web video highlighting what it points to as falsehoods from the candidate's past. The video came with a lengthy memo (posted on the site and distributed to reporters), which noted that self-identified fact checkers like PolitiFact and The Washington Post make the same argument about several of Romney's remarks. On Tuesday, the group began releasing a slew of opposition research documents about Romney's positions on a range of policy areas, and it plans to release 20 in all by the start of the debate.

"We're planning to use our archive of research and video to set the record straight on Romney's inevitable distortions Wednesday night," said American Bridge spokesman Chris Harris.

Once the debate is over, American Bridge will fire off a series of rapid response videos highlighting when it thinks Romney veered—even slightly—from the truth. And it will have on hand its media and research staff to react to anything unexpected that may have happened during the live debate.

At least for this first debate, other major Democratic outside groups will be looking to American Bridge to spearhead fact checking and research, since it has one of the most comprehensive troves of material. It expects the Democratic Party to handle the traditional rapid response operations, so it can focus on disseminating its video archives. Other groups have different missions. Priorities USA Action, a Democratic super PAC established in 2011 by former Obama aides, will have its leaders go on television and radio.

Meanwhile, Republican outside groups certainly don't plan to sit on the sidelines Wednesday, but the top conservative super PACs aren't planning as comprehensive of an ambush surrounding the debate. American Crossroads, a prominent conservative super PAC, will release a Web video that highlights Obama's own whoppers while a team of researchers prepares rapid response letters to blast out to members of the media. It also will post live updates about the debate on Twitter to back up Romney online. Restore Our Future, the main super PAC supporting Romney, declined to comment about its debate plans.

The goal of the strategy for both sides, of course, is to undercut the opposing candidate's integrity before the debate moderator utters a single question. While super PACs are not legally allowed to coordinate with candidates, their work will serve as a supplement to the campaigns and the political parties behind them, which will already be spinning the debate throughout the night.