Aaron Fielding quietly stalks his prey - Republicans - with his video camera, patiently waiting for a political moment worthy of YouTube.

At 27, he is a full-time "tracker" for American Bridge 21st Century, a new Democratic organization that aims to record every handshake, every utterance by Republican candidates in 2011 and 2012, looking for gotcha moments that could derail political ambitions or provide fodder for television advertisements by liberal groups next year.

The organization has hired a dozen professional trackers like Mr. Fielding, outfitted them with the latest high-tech cameras and computers and positioned them in key states where Republican candidates are busy chattering away to voters. If all works as planned, incriminating moments captured by American Bridge will quickly become part of the political bloodstream.

Combined with a team of 20 researchers in a Washington "war room" that has a large rack of computer servers, the effort is part of a push by Democratic groups to bolster their opposition research. Republicans also have trackers, but so far have not assembled the kind of centralized video archive of political caught-on-tape moments that their rivals envision.