The prosecution's key witness returns to the stand today in the trial of John Edwards. Andrew Young, a former campaign staffer, claims the former presidential candidate was fully aware of the nearly $1 million from two wealthy donors used to hide his pregnant mistress during his 2008 bid for the White House.

But Young, who initially claimed paternity of Edwards' illegitimate child, continues to pose problems for the prosecution. Yesterday, the judge indicated that in recent days the former Edwards aide had improperly contacted three other witnesses in the trial to ask what they planned to say and that Young had a one-night stand with one of the witnesses back in 2007.

"They're taking a bit of a risk by putting their key witness on the stand first," said Kieran Shanahan, a Raleigh, NC lawyer and former federal prosecutor who is attending the Edwards trial. "If in cross examination they're able to destroy his credibility, it'll be very difficult for the government to recover."

Prosecutors are trying to prove that the funds in question were not just private gifts to hide Edwards' affair from his cancer-stricken wife, but actual campaign contributions intended to prevent the affair from damaging his bid for president. They plan to play voicemails Edwards left on Young's phone during the campaign.

The defense claims the secret payments were not intended to influence the outcome of the election, but to spare Edwards' family pain and embarrassment. Edwards' lawyers also allege that Young used much of the money to build an upscale house for himself in Chapel Hill, NC.

"The defense took a great position in opening statements by saying, 'Follow the money,'" Shanahan said. "Much of this alleged $1 million in fact went to Mr. Young and to his family."

Edwards faces six criminal counts of campaign finance violations for allegedly accepting, and failing to report, campaign donations in excess of the $2,300 limit for individual contributions. Each count carries a maximum sentence of five years in prison and a $250,000 fine.