Federal investigators are looking into Hillary ClintonHillary Diane Rodham ClintonTrump adds to legal team after attacks on Mueller Press: You can’t believe a word he says Feehery: March Madness MORE's 2008 presidential race as part of a deeper investigation into a D.C. businessman alleged to have financed multiple "shadow" campaigns, including one to boost Clinton's performance that year.

According to a Washington Post report, the federal investigators are looking into whether businessman Jeffrey Thompson invested more than $600,000 into an off-the-books effort to get out the vote for Clinton in four primary states. 

The report said prosecutors do not expect to pursue a separate criminal case against Clinton's campaign. 

Investigators have interviewed more than a dozen Clinton campaign staffers and supporters and reviewed hundreds of emails, with questioning focused largely on a senior adviser, Minyon Moore, and her role organizing the unofficial "street teams" that Thompson funded.

The Post reports that Moore is part of a "close-knit circle of advisers" who have discussed the possibility of Clinton running again in 2016.

As a senior adviser on Clinton's 2008 campaign, Moore conducted minority voter outreach, among other responsibilities. She connected marketing executive Troy White — who organized the get-out-the-vote "street teams" in Texas, Indiana, North Carolina and Pennsylvania — with Thompson, who funded them.

Campaign finance law bars such efforts if they are found to be an undisclosed, in-kind campaign donation that exceeds federal contribution limits.

In Texas, according to the Post, Moore provided White with confidential internal campaign documents, as well as campaign paraphernalia.

A statement issued on her behalf by Moore's employer, Dewey Square Group, said she "was entirely unaware of any inappropriate activities” and is cooperating with the investigation.

It's unclear whether the street teams made an impact on the race in the Lone Star State, which Clinton ultimately won. It was, at the time, a must-win for the lagging candidate, but Obama managed to pull more delegates from the state by winning more of the party caucuses.

Multiple former staffers interviewed by The Washington Post said they were unaware of any such get-out-the-vote effort taking place behind the scenes of the Clinton campaign.

An attorney for Clinton's 2008 campaign said the campaign "has cooperated fully" in the investigation.

The Post report indicated the investigation is part of an effort to expand a corruption case against Thompson.