What is opposition research?

NEW YORK (FOX 5 NEWS) - Donald Trump Jr.'s admission that he met with a Russian attorney in hopes of getting dirt on Hillary Clinton is putting the once-shadowy field of opposition research into the spotlight.

Details mined from opposition research have played prominently in past campaigns. Think John Edwards' $400 haircut. A researcher for then-Sen. Barack Obama's campaign stumbled on the expenditure in a campaign finance report and passed it along to Politico.

A 2012 video of Mitt Romney criticizing Obama voters, telling donors 47 percent of Americans are dependent on government assistance was discovered by a freelance researcher and went viral after it was posted on Mother Jones.

Days before the 2000 election came word that George W. Bush had once pled guilty to DUI. This too was courtesy of "oppo" research.

We spoke with a former opposition researcher about what the process entails.

"A lot of researchers are typical research nerds hanging out at desks all day, trolling LexisNexis, the SEC, any government website a candidate or elected official has ties to, based on records," said Daniel Knight, who has done opposition research for the National Republican Congressional Committee and America Rising, a political action committee.

"We don't see it as the dark arts where we're digging up dirt and slinging it and just destroying campaigns," Knight said. "We see it as actually exposing people for who they are."

The search for opposition research typically extends beyond the Internet to remote courthouses and libraries. But it usually doesn't come from foreign governments, and that is where Don Jr.'s efforts cross the line, according to political analysts.

"It is unheard of to get opposition research from a foreign government to smear someone else in a political campaign." said Hank Sheinkopf, a veteran campaign strategist.

The constant churn of social media and the 24-hour news cycle have created more platforms for opposition research than ever. Now there are entire political action committees and private firms dedicated solely to deep political digging.