A new Jonnie R. Williams Sr. emerged on the witness stand Friday at the federal corruption trial of former Virginia governor Robert F. McDonnell and his wife, Maureen.

Instead of the confident, assured executive who on Thursday described with great specificity how he had persuaded the McDonnells to sell the governor’s office, this Williams said he could not recall the details of several conversations and meetings, including one that occurred on Sunday.

On the first full day of Williams’s cross-examination, attorneys for the former governor and for his wife tried to hammer away at Williams to poke holes in the prosecution’s theory of a conspiracy.

Williams’s account of his interactions with the first couple remained largely consistent. But again and again, he acknowledged that he had no way of knowing whether the governor was aware of many of his interactions with the first lady or her promises that the couple would help Williams’s dietary-supplement company.

In addition, he said repeatedly that he could not remember details of various meetings he has had with law enforcement since he was first approached in January 2013.

Prosecutors in the corruption case against former Virginia Gov. Robert McDonnell and his wife, Maureen, introduced the infamous Rolex watch on Thursday as a key piece of evidence in the trial. The Post’s Rosalind Helderman explains. (Jackie Kucinich/The Washington Post)

Friday marked the second full day that Williams held the stand at the trial. The McDonnells have been charged with 14 counts of public corruption and lying on loan documents.

At times, the executive was evasive and combative; at others, he was quick-witted and downright funny, appearing to charm jurors, who occasionally cracked smiles at his jokes. His turn on the stand is not complete: Defense attorneys will pick up their cross-examination of Williams, the former chief executive of Star Scientific, on Monday.

Defense attorneys have asserted that the McDonnells’ marriage was crumbling in 2011 and 2012, when Williams claims he came to an understanding with the two that he would provide luxury gifts, vacations and large loans in exchange for their help promoting Star’s latest product.

But the couple barely spoke, their attorneys say, and therefore could not have been conspiring to assist Williams, as prosecutors have claimed. The first lady had even developed a crush on the wealthy businessman, her attorney said. The governor himself, defense attorneys say, was largely unaware of his wife’s interactions with Williams.

In certain instances, Williams agreed Friday that he could not refute that claim.

He said, for example, that he did not discuss with the governor what Maureen McDonnell had said at Star events in Michigan and California in 2011, where video shows she told doctors that she and her husband were both excited about the company.

Williams likewise agreed that it was Maureen McDonnell, not her husband, who told him in 2012 that the governor wanted to know the names of University of Virginia officials who were dragging their feet on conducting studies of Williams’s new supplement. Williams said, too, that he did not discuss a launch event for the product held at the governor’s mansion in August 2011 with Robert McDonnell. He instead planned it with the first lady and her chief of staff. The governor ultimately attended the luncheon.

As for his many gifts, Williams said he never alerted the governor that he had taken Maureen McDonnell on a $20,000 shopping spree in New York in April 2011, even though he later told law enforcement that the encounter was the “most awkward event” of his life and that the first lady had acted “like a kid in a candy store.”

He also said that the governor did not specifically ask for the use of his Ferrari when the McDonnell family enjoyed a July 2011 vacation at Williams’s Smith Mountain Lake home.

He said it was possible that McDonnell arrived at the house after the car had arrived, as requested by the first lady. (When asked about the Ferrari last year, a spokesman for McDonnell said the governor had driven the car to Richmond from the lake house as a favor to the executive.)

Williams said he purchased a Rolex watch for the governor at Maureen McDonnell’s request in 2011 with the understanding that she was planning to give it to her husband as a Christmas gift. As for whether her husband knew the true origins of the watch, he said, “that’s between the two of them.”

Still, Williams stood by his account that McDonnell had personal involvement with the alleged scheme throughout. He said he laid out for the governor how he wanted state government to help his company on a flight of more than five hours from California in 2010.

Later, he insisted, he discussed with the governor a $50,000 loan he was extending to the first lady before he wrote the check.

And it was the governor himself who asked Williams for an additional $70,000 to benefit a small real estate company McDonnell owned with his sister in 2012, exchanging personal texts and meeting alone with the businessman in the governor’s office suite to discuss specifics.

As the first week of the trial concluded, some of the most lurid and embarrassing details yet emerged from a spectacle that has already been full of them.

Maureen McDonnell’s defense attorney William Burck, who has claimed that his client had romantic feelings toward Williams, showed him an e-mail the first lady sent him Aug. 23, 2011, the day of an earthquake that could be felt throughout Virginia.

“I just felt the EARTH MOVE AND I WASN’T HAVING SEX!!!!” she wrote.

“I don’t recall ever seeing this,” Williams responded when he was shown the note, “though it’s funny.”

At another moment, Williams was asked about a note written by Maureen McDonnell in 2013, which he received in a box along with dresses he had purchased for her two years earlier. In the note, she wrote that she “truly hoped” his daughter would enjoy the dresses and, if the daughter didn’t, suggested giving them to one of many worthy charities to sell, “like we talked about.”

He earlier had testified that he knew the note was a “fabrication” that arrived only after both had been interviewed by law enforcement because it indicated that the two had agreed that she would return the items to Williams. Maureen McDonnell has been charged with obstruction of justice for sending it.

“Either one of my children is a size zero,” he said. “These dresses were never intended to be given back to my daughters.”

Williams’s memory appeared to fade when discussing his sessions with law enforcement, who first questioned him about the McDonnells, as well as various potential securities violations, in 2013.

He said Thursday that he had lied in that initial meeting, insisting that he had never asked the McDonnells for anything and wanted nothing from them. He cut the interview short, he testified Friday, when a Virginia State Police officer asked him to wear a wire against the governor.

Williams is now testifying under a deal that gives him immunity from prosecution both for his dealings with the McDonnells and for other matters.

Often, Williams simply claimed that he could not remember various things that defense attorneys said happened, saying “I don’t recall” several times.

He even pleaded confusion and lack of memory when it came to a meeting with prosecutors Sunday — the day before the trial began — to discuss some type of “share transactions” and his fear that he had done something wrong with those.

Burck asked: “Mr. Williams, did you tell the prosecutors on Sunday, less than a week ago, that you did not want share transactions disclosed” because there might be legal issues?

“I may have. I don’t recall,” Williams responded, after asking for clarification and the question to be repeated.

Perhaps most notably, he denied that he and Maureen McDonnell had exchanged a series of late-night texts one night in May 2011, although phone records seemed to show they shared eight messages between 1 a.m. and 8 a.m.

“I don’t do this, and I did not have these calls and texts in the middle of the night,” he said.

A few times, Williams elicited genuine laughs from the packed courtroom and smiles from jurors. One back-and-forth was particularly memorable.

After Williams testified that he had been “uncomfortable” spending more than $6,000 on a Rolex watch for the governor’s wife to give to her husband, Burck asked if the businessman had a similar feeling when, in 2009, he bought a $5,000 bottle of cognac to share with a few of the governor’s staffers.

Williams testified that he did not and made reference to a male model friend who also shared the liquor. Burck asked: If the male model had been present when Maureen McDonnell asked for the watch, would that have put him at ease?

“That’s outrageous,” Williams deadpanned.

And the comedy continued. Burck asked Williams if he had, in fact, poured some of the cognac into a fireplace. The businessman flashed a sheepish smile.

“There was a little bit left,” he said. “I was curious what it would do.”

Justin Jouvenal and Rachel Weiner contributed to this report.