The pressure of responding to attacks is unusually intense this election cycle because of the number of plausible contenders in both major political parties.

"It's become a multi-front war," said David Bossie, president of the conservative advocacy group Citizens United. "Candidate A attacks candidate B, but then C and D pile on. You have to be on your toes at all times."

Campaign finance records show that the candidates have spent more than $110,000 on subscriptions to the Nexis-Lexis family of databases over the last year. Most of the leading candidates employ half a dozen researchers, combing the records of their rivals for the smallest mistake. All the campaigns are constantly shoveling out "fact checks" pointing out the errors of rival candidates.

Opposition research has been a staple of political campaigns for decades, but the Internet and blogs have made it easier to disseminate the information. Tracking video of embarrassing moments collected by rival campaigns is now routinely distributed on YouTube. When the Democratic National Committee unveiled "Flipper TV," a new Web site devoted to tracking video from Republican political events, in November it got 60,000 hits the first day.

Despite the increasing risk of getting caught, mistakes, exaggerations, and fibs are still plentiful. "Political candidates have been misleading voters for more than 2,000 years," said Jackson, the Annenberg fact checker.