A longtime aide to former Virginia governor Robert F. McDonnell drew a stark contrast between her boss and her boss’s wife at the couple’s trial Monday, describing the onetime Republican rising star as “Mr. Honest” and the former first lady as a manager so ­“diva-ish” that her staff once threatened to quit en masse.

The testimony from former secretary of the commonwealth Janet Vestal Kelly came on the first day of the McDonnells’ defense. It could help both Robert and Maureen McDonnell as they fight corruption charges.

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While personally unflattering to the former first lady, Kelly’s assertions seemed to support the defense argument that the McDonnells’ marriage was troubled and the governor did not know everything his wife did.

The McDonnells are charged with 14 counts of public corruption, lying on financial documents and obstruction of justice stemming from their relationship with Richmond businessman Jonnie R. Williams Sr., a wheeling-and-dealing former dietary-supplement company executive. Prosecutors say that Williams lavished loans, vacations and luxury goods on the McDonnells to get the power of the governor’s office behind his company and its supplement, Anatabloc.

List of gifts given to the McDonnell family from Jonnie Williams.

Though Kelly’s assertions about Maureen McDonnell were perhaps the most dramatic of Monday’s testimony, attorneys also began a methodical defense to convince jurors that, despite his generosity, Williams and his company, Star Scientific, received nothing in return. Several former cabinet members testified that Williams never got what he wanted.

Kelly was able to provide particular insight into the McDonnells’ relationship and character because of the length of her personal and professional relationship with the two. She said that her professional career has revolved almost exclusively around the former governor’s, starting when she worked as a volunteer on his reelection campaign for a state delegate seat in the late 1990s.

After McDonnell became governor, Kelly was responsible for the state’s 4,000 board appointments. She testified that the governor never asked her to put Williams in any of those positions. She also went to great lengths to praise her former’s boss’s integrity and said others seemed to share her positive view.

“The common thread in all of those communities is that if they had to elect a Boy Scout of the year, Mr. Honest, it would be him,” Kelly testified.

Kelly did not seem to think as highly of his wife.

While claiming to be “personally very fond of Maureen,” Kelly testified that she and others found the first lady to be so difficult to work with that consultants from Virginia Commonwealth University were brought in in late 2011 to improve working conditions in the governor’s mansion. And in January 2012, Kelly said, she got word that mansion staffers intended to give a letter to Maureen McDonnell in which they “all threatened to quit en masse.”

Kelly said she intercepted the staffers before they could go to the office of the governor’s chief of staff, and she and a consultant discouraged them from delivering the letter. Kelly said while she agreed with its sentiments, she did not think the note would have any effect on the first lady.

“I think she was pathologically incapable of taking any kind of responsibility,” Kelly said.

The testimony is important because it draws a strong difference between the first lady’s behavior and that of her husband and lends credence to the defense assertion that Maureen McDonnell sometimes operated behind her husband’s back. Kelly also testified that it was “well known” that the first lady would “hide things.” She said some feared the first lady even had some type of mental illness.

Kelly also supported the so-called crush defense — the notion that Maureen McDonnell was perhaps romantically interested in Williams and was seeking his affection rather than his money. Kelly testified that the two were “kind of flirty” on a flight to South Carolina.

But Kelly acknowledged under cross-examination that she had not mentioned any flirtation to prosecutors earlier. In fact, prosecutors said, Kelly had laughed when investigators asked in an interview if she had heard rumors that the first lady was having an affair with Williams. “In some ways, I wish I had [heard rumors], because that would explain everything,” Kelly said she had told investigators.

At the same time, Kelly appeared to hold some sympathy for the governor’s wife, breaking down in tears at one point because she did not want to “pile on” against the first lady. Kelly testified that Maureen McDonnell repeatedly told her that being first lady was not something she had wanted. She was uncomfortable with public speaking and, in her first year in the mansion, lost both her parents and sent her youngest children to college — all while essentially losing her husband to his job.

“She would say, ‘I didn’t sign up for this. This isn’t what I wanted,’ ” Kelly testified. “It was a lot for her.”

Prosecutors seemed to take aim at Kelly’s glowing characterization of her former boss, asking the former cabinet secretary if she knew of the tens of thousands in loans he had received from Williams or of the conversations the two men allegedly had about Anatabloc. She said she did not, though she said she was aware of $15,000 that Williams had given for catering at one of the McDonnells’ daughter’s weddings “in quasi real time.”

In the afternoon, defense attorneys presented a parade of former McDonnell cabinet secretaries to testify to all the things McDonnell could have done to assist Williams and his company. In turn, each witness agreed that McDonnell never took those actions.

Laura Fornash, who as secretary of education served as the administration’s chief liaison to public colleges and universities, said she was never asked to intervene at the University of Virginia or Virginia Commonwealth University to urge researchers to study Anatabloc.

Finance secretary Richard D. “Ric” Brown said McDonnell never sought to insert money for the company into the state budget. Former secretary of commerce and trade James Cheng said McDonnell never sought legislation to assist Star, as he did for several other companies. He also never sought to give the company an economic incentive grant from funds over which he had near sole discretion, Cheng said.

All three indicated that the governor commonly asked them to meet with executives from private companies, as he asked them to do with Williams.

This report initially referred to Richard D. “Ric” Brown as former finance secretary. Brown continues to hold the post.

Justin Jouvenal and Rachel Weiner contributed to this report.

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