Former Virginia governor Robert F. McDonnell (R) and his wife arrived at their first court appearance hand in hand — a public showing of unity in the face of federal corruption charges. When the former governor’s attorneys filed legal motions, his wife’s attorneys generally joined them, the two appearing to move in lockstep.

But Tuesday night, the couple asked a judge to order two separate trials, saying it would be unfair to have a single jury decide both cases.

Only then, they said, would Maureen McDonnell agree to testify — without fear of incriminating herself — that her husband was largely unaware of her dealings with the wealthy Richmond businessman at the center of the prosecutors’ case. And only then, they said, would Robert McDonnell be able to testify on his own behalf without his wife silencing him through marital privilege.

The move, legal experts say, is a clever legal strategy that could benefit both of them. With Maureen McDonnell’s help, Robert McDonnell might be able to cast himself as a husband in the dark, instead of a scheming politician who worked with his wife to help a wealthy benefactor.

And if her husband is cleared, Maureen McDonnell could argue that she was unable to lend any assistance to benefactors because she was not a public official. Jurors, legal experts said, may be sympathetic to a wife who wasn’t the one elected.

“The government has to take this seriously,” said Scott Fredericksen, a lawyer at the Foley & Lardner firm, who is not affiliated with the case. “If she’s not sitting there, I think it increases his chances of being able to portray the case as involving his wife, and not the governor. . . . Let’s say, if he wins, are they really going to want to go after the governor’s wife now?”

To be sure, arguing that Robert McDonnell knew little about his wife’s conduct is not a silver bullet for the defense. Prosecutors have alleged the former governor benefited in many ways directly from the largesse of Richmond businessman Jonnie R. Williams Sr. in exchange for McDonnell’s lending the prestige of the governor’s office to him and Star Scientific, the company he used to run.

While prosecutors have alleged in a 14-count indictment that Williams filled Maureen McDonnell’s closet with designer clothes, they also have said that Robert McDonnell and his sons ran up the bill on Williams’s tab at a Virginia golf course. And prosecutors have alleged that the former governor talked to Williams personally about a loan for a struggling rental property in Virginia Beach.

In exchange, prosecutors have alleged, Robert McDonnell hosted a product launch for Star’s dietary supplement, Anatabloc; promoted it at public events; arranged meetings between Williams and senior state health officials; and worked with his wife to encourage state researchers to consider conducting trials of the product.

Robert McDonnell and his attorneys have long insisted that the former governor was not completely aware of his wife’s dealings with Williams, and Maureen McDonnell told prosecutors last summer that she felt responsible for the couple’s relationship with the businessman.

Both Robert and Maureen McDonnell have pleaded not guilty, and a jury trial is scheduled for July 28.

In the motion to sever the cases, Robert McDonnell’s attorneys wrote that Maureen McDonnell was willing to testify that her husband “had no timely knowledge of many of her interactions with Williams” — but only if the trials were separate. Maureen McDonnell’s attorneys endorsed the motion.

Defense attorneys wrote that Maureen McDonnell’s relationship with her husband was “strained,” in part because of the former governor’s demanding work and travel schedule, and that she and her husband did not act “in concert” when it came to Williams.

If the couple were to be tried together, the attorneys wrote, Maureen McDonnell would invoke her Fifth Amendment right not to testify, and she would invoke the marital privilege doctrine to prevent her husband from sharing details of their private conversations. The attorneys said that was especially unfair because it impeded Robert McDonnell’s ability to testify in his own defense.

Legal experts unconnected to the case said U.S. District Judge James R. Spencer will ultimately decide whether to separate the proceedings.

Although the filings did not detail what Robert and Maureen McDonnell would say if they testify, their attorneys said that both would be able to directly dispute some of the prosecutors’ allegations. Experts cautioned, though, that the filings do not guarantee that either will take the stand, even at separate trials.

Peter Zeidenberg, a former federal prosecutor now in private practice at the DLA Piper firm, said that separate trials would give the former governor and his wife the opportunity to “throw dirt on the other without them both sitting there and getting it all over.” At a joint trial, he said, it would be difficult to convince jurors that no one did anything wrong if both were “pointing the finger at each other.”

If the trials are separate, legal experts said, which is held first would be significant. If Maureen McDonnell’s trial came before her husband’s, she would be able to invoke her Fifth Amendment and marital privilege rights during that proceeding, then change course for her husband’s trial, legal experts said.

If Maureen McDonnell’s trial followed her husband’s, though, prosecutors might try to introduce as evidence any statement she made at the previous trial, said Andrew T. Wise, a lawyer at Miller & Chevalier. “It certainly is a strategy with some risk,” he said.

Still, trying Maureen McDonnell alone might come off as “heavy handed” because she was not an elected official, said Peter H. White, a former federal prosecutor now at the Schulte Roth & Zabel firm.

And if Robert McDonnell were to be acquitted, the Justice Department might face pressure to drop the charges against his wife, said Edward Kang, a lawyer with the Alston & Bird firm.

As of Wednesday afternoon, a judge had not ruled on the request, and prosecutors had yet to respond. A Justice Department spokesman declined to comment, and defense attorneys did not respond to phone messages.