GREENSBORO, N.C. — Tempers were short Thursday as the grueling cross-examination of the government's lead witness continued in the campaign finance violations case against two-time presidential candidate John Edwards.

Edwards, a former U.S. senator from North Carolina, is charged with conspiracy, filing false campaign reports and four counts of accepting illegal campaign contributions in connection with the nearly $1 million two donors secretly paid in 2007-08 to hide Edwards' pregnant mistress, Rielle Hunter, as he ran for the White House.

During his fourth day on the witness stand, former Edwards aide Andrew Young continued to battle defense attorney Abbe Lowell at every turn as Lowell questioned Young's timeline of events in an attempt to undermine his credibility.

The defense has told jurors that Young is the person who schemed to get the bulk of the money from Rachel "Bunny" Mellon, an elderly heiress in Virginia, so he could finance a lavish lifestyle and that Edwards knew nothing about it. The rest of the money, the defense said, was a gift from Texas trial lawyer Fred Baron, who was Edwards' campaign finance chairman, and wasn't a political contribution.

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Lowell repeatedly asked Young when and where conversations with Edwards occurred about securing money to keep Hunter quiet. Young seemed confused by some questions, said he couldn't recall the specifics of various incidents and often asked Lowell to repeat himself.

"Never mind, I'm withdrawing the question," a frustrated Lowell snapped at one point.

During a line of questioning about when and how Young learned of Hunter's pregnancy, U.S. District Judge Catherine Eagles expressed her own frustration with the pace of Lowell's argument, which appeared to have some jurors nodding off.

"You're about to beat a dead horse," an impatient Eagles told him.

Lowell suggested that Hunter never planned to expose the affair, so there was no reason to pay her off. Instead, he said, Young used the affair as leverage to remain close to Edwards and obtain money for himself.

"Isn't that just another way to have Mr. Edwards indebted to you?" Lowell asked about Young's initial claim that he was the father of Hunter's baby.

"That was not the thought process at that point," Young responded. "This was putting out a fire."

After Young publicly made the claim – he says it was Edwards' idea to keep the media at bay during the early 2008 caucuses and primaries – he and his family jetted across the country, staying at resorts in south Florida and San Diego and at Baron's estate in Aspen, Colo.

Lowell suggested the adventure was like a vacation for Young, and for once, the witness agreed.

The defense also pointed out Young's spending on a $1.5 million home he was building in Chapel Hill, noting various change orders added a pool and a home theater at the time that money from Mellon was pouring into his bank account.

"We lost our sense of perspective," a somber Young acknowledged.

Lowell also brought up incidents involving an ATM card and a cellphone, nicknamed the "Batphone," that Edwards and Hunter used to communicate.

Elizabeth Edwards routinely checked the monthly records of personal and campaign cellphones after learning that her husband was having an affair, Young has said, so a special cellphone was needed. Likewise, Elizabeth Edwards was livid when she learned that her husband had allowed Hunter to use his ATM card on a shopping spree, according to testimony.

Lowell suggested that the two incidents pointed to John Edwards' need to hide his affair from his wife, not to get money for his campaign.

"Every dollar (from Mellon and Baron) went to you or your wife's account," he said to Young.

"That is correct," Young replied.

The cross-examination is expected to continue Friday, when Young's wife, Cheri, could also be called as a witness for the prosecution.