Rep. Duncan D. Hunter will rely on what experts called a shaky legal defense as he battles charges of illegally using campaign money to subsidize overseas vacations, expensive dinners and extramarital “personal relationships.”

Hunter’s legal case was dealt a blow last week when his wife, Margaret Hunter, pleaded guilty to one count of corruption in the couple’s pending case.

Also challenging for Hunter is his attorney’s announcement that he will defend his client using the “Speech or Debate” clause, which legal experts say doesn’t apply in his case.

The Republican congressman and his wife, who also served as his campaign manager, were indicted last year on more than 60 criminal charges for dipping into campaign coffers when their personal accounts were overdrawn.

Margaret Hunter’s plea agreement shows that she is supplying information to the prosecution as it builds a case against the congressman, legal experts say. She will be required to “make a good faith effort to provide substantial assistance to the United States in the investigation and prosecution of others,” according to the terms.

[Opponent pounces after Duncan Hunter’s wife switches to guilty plea]

“It’s not good news for Duncan Hunter,” said Laurie Levenson, a former federal prosecutor and a professor at Loyola Law School. “I suspect she will be very helpful.”

The couple conspired to steal more than $250,000 in donor funds as “petty cash” for routine household expenses such as groceries, according to federal prosecutors. They also spent the money on luxury items which included Hawaiian shorts and travel expenses for a pet rabbit named Eggburt.

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Spousal privilege 

Husbands and wives have certain rights to avoid incriminating their spouses, but those marital privileges will probably not be an obstacle for the prosecution, according to Levenson.

Emails and texts between spouses are in some cases off-limits to the court, but communications in furtherance of a crime or fraud are exempt from that rule.

And though Margaret Hunter could refuse to testify against her husband, her plea agreement states that she has waived that right.

“The only wildcard is, when she testifies, how much of the dirty work will she point the finger at him for? And to what extent will she implicate herself and fall on the sword?” Levenson said.

Margaret Hunter’s decision to not shield her husband may have been in part motivated by a revelation laid out in the plea agreement: Duncan Hunter spent some of the funds to maintain several “personal relationships” with people living in D.C., including someone who worked with him, and concealed that spending from his wife.

[Duncan Hunter’s ‘personal relationships’ get new attention in indictment]

‘A complete loser’

As word of the plea agreement broke, Gregory Vega, attorney for Duncan Hunter, waived the bad news. He announced plans to argue that the U.S. Constitution’s “Speech or Debate” clause protects lawmakers such as Hunter.

“We are aware of Mrs. Hunter scheduling a hearing to change her plea. At this time, that does not change anything regarding Congressman Hunter. There are still significant motions that need to be litigated, specifically the Speech or Debate Clause of the U.S. Constitution,” Vega said in a statement to several media outlets.

At least nine lawmakers have invoked the clause in a bid for immunity from a range of criminal behavior, including bribery, corruption and money laundering, according to the Buffalo News. None were exonerated. Republican Rep. Chris Collins of New York has recently invoked the Speech or Debate Clause in an effort to access reams of the prosecution’s evidence  in his battle against insider trading charges, the paper reported. 

[Are lawmakers ‘supercitizens’? Constitutional question could delay Rep. Chris Collins case]

The clause states that “for any Speech or Debate in either House,” members of Congress “shall not be questioned in any other Place.” It’s designed to maintain a balance of powers between the branches of government by protecting the legislative from punitive prosecution by the executive or judicial branches.

In Hunter’s case, legal experts say it’s an especially shaky approach.

“I think it’s a complete loser. I can’t see how a campaign finance case has Speech or Debate implications,” said Melanie Sloan, an expert in congressional ethics and former federal prosecutor.

The clause covers actions taken by the member of Congress in the course of legislating. Hunter’s case deals with misspending donations to his campaign.

“The Speech or Debate clause deals with the legislative sphere,” Sloan said. “That includes things people say on the House floor, or things they learn through their positions on committees. It doesn’t apply to the campaign sphere.”