Prosecutors had called their first witness, and Senator Robert Menendez’s blame-my-wife strategy in his federal bribery trial already appeared vulnerable.

An F.B.I. agent was testifying about a search of the New Jersey home that Mr. Menendez, 70, shares with his wife and the gold bars that were found inside a locked bedroom closet — bribes prosecutors say were paid to the couple in exchange for political favors by the senator.

Although the closet held women’s clothing, the agent said, a man’s blue blazer was also found hanging inside, seemingly tying Mr. Menendez to the gold and other alleged bribes. The agent stuck by his account even after Mr. Menendez’s lawyer, during cross-examination, pressed him and displayed a photograph showing the blazer hanging outside the closet.

But the next morning, the agent asked to clarify his testimony. After reviewing photographs of the search, he said, he agreed the blazer was hanging outside the closet.

Was his previous day’s testimony no longer accurate? Mr. Menendez’s lawyer asked.

“That is correct,” the agent said.

The moment passed quickly, but the exchange illustrated what has become a central pillar of Mr. Menendez’s defense: shifting blame to his 57-year-old spouse, Nadine Menendez, as he stands trial accused of trading political favors for hundreds of thousands of dollars in cash and gold.

The strategy, unusual and even startling when Mr. Menendez’s lawyers first said they would use it, is not without precedent in American courtrooms. But the approach carries significant risk, legal experts said, not least because it has the potential to offend jurors.

Paul Shechtman, a longtime New York defense lawyer who lectures at Yale Law School, said that unless there is evidence in a case pointing strongly toward a defendant’s spouse, a jury is unlikely to be sympathetic to an attempt to shift blame.

“One worries that the jury will say you’ve committed two crimes — you’ve taken bribes and you’ve blamed your spouse,” Mr. Shechtman said.

Prosecutors have portrayed Robert and Nadine Menendez as partners in a complicated web of corruption. Together, they are accused of conspiring to accept gold, cash, a Mercedes-Benz and other bribes collectively worth hundreds of thousands of dollars in exchange for the senator’s helping three New Jersey businessmen and the governments of Egypt and Qatar.

Ms. Menendez appears conspicuously in the indictment, both in the way it describes her relationships with the businessmen and the benefits it says she received. She had known one of the businessmen for years before her marriage to the senator. Two of them helped to pay off her mortgage debt and bought her the Mercedes, the indictment says. One of them promised to place her on the payroll of his company in a low- or no-show job.

The U.S. attorney’s office for the Southern District of New York has not directly addressed the senator’s courtroom strategy of trying to persuade jurors that his wife was to blame, but a prosecutor, Lara Pomerantz, told the jury in an opening statement that Mr. Menendez “was careful when he was committing crimes.”

“He was smart enough not to send too many texts,” Ms. Pomerantz said. “Instead, he had Nadine do that for him. And sometimes, as you will see, he told her not to put things in writing.

“He used Nadine as his go-between to deliver messages to and from the people paying the bribes,” she added.

Mr. Menendez’s lawyers have sought to portray the senator as living largely separately from his wife. They had separate bank accounts, credit cards and cellphone plans.

Mr. Menendez’s lawyer, Avi Weitzman, told the jury in his opening statement that before their marriage, Nadine Menendez hid her money problems from her new boyfriend, keeping him “in the dark on what she was asking others to give her.”

“She tried to get cash and assets any which way she could,” Mr. Weitzman said.

Mr. Weitzman, foreshadowing the cross-examination of the F.B.I. agent, also told the jury that Senator Menendez did not have a key to his wife’s locked bedroom closet, nor did he know she kept gold bars there.

“It is Nadine’s closet,” Mr. Weitzman said. “In fact, when you look inside the closet, you will see that it is filled with all of Nadine’s clothing. Women’s clothing.”

Martin S. Bell, a former Southern District corruption prosecutor who is now in private practice, said the emerging narrative in the Menendez trial shows why the blame-my-wife defense may have been attractive to his lawyers.

“When a door opens that leads to any other explanation — the behavior of a spouse, a closet space belonging to a partner — you start to see daylight like a running back,” Mr. Bell said. “It’s hard not to run in that direction.”

Mr. Menendez’s lawyers, in a pretrial court filing, said they might have to argue, in effect, that any unlawful conduct that may have occurred — “and we are aware of none — involved the actions of others (including Nadine), not the senator.”

Lawyers for Mr. Menendez and his wife each declined to comment Wednesday on the senator’s defense strategy.

In pointing the finger at Ms. Menendez, the senator’s lawyers are echoing a strategy used a decade ago by lawyers for Bob McDonnell, a former Republican governor of Virginia who was tried with his wife, Maureen, on charges they accepted more than $170,000 in loans and gifts from a nutritional supplements executive in return for political favors.

In a closing argument, the governor’s lawyer, Hank Asbill, portrayed the couple’s marriage as “too dysfunctional” for them to have conspired criminally, and he pinned blame on Ms. McDonnell for becoming infatuated with the executive, Jonnie R. Williams Sr.

“Logical or not, Maureen misled Bob, or didn’t tell Bob things relating to Jonnie Williams and money,” Mr. Asbill said.

The prosecutor told the jury that Mr. McDonnell was “willing to throw his wife under the bus, and she’s willing to let him, in order to avoid criminal convictions.”

The McDonnells were both found guilty, but in a landmark 2016 decision, the U.S. Supreme Court unanimously overturned the verdict and narrowed the definition of conduct that constituted official corruption.

Carrie H. Cohen, a former corruption prosecutor and once chief of the public integrity unit of the New York attorney general’s office, said Mr. Menendez’s defense appears right out of the McDonnell playbook. Both men, Ms. Cohen noted, had a wife who “liked finer things and finer cars,” and each man claimed his wife acted without his knowledge.

“We’ve seen how this plays out,” Ms. Cohen said. “It is a good defense to blame the spouse.”

Ms. Menendez relied mainly on alimony and child support after her 2005 divorce, court records show. By 2018, when she and Mr. Menendez began dating, she was unemployed and behind on her home mortgage payments. Then, police records show she was involved in a fatal pedestrian crash, leaving her without a car. A businessman who was charged with the couple and pleaded guilty in March has admitted providing Ms. Menendez with a Mercedes to replace her wrecked car — and to influence the senator.

Unlike the McDonnells, Mr. Menendez and his wife are being tried separately. The judge, Sidney H. Stein of Federal District Court, postponed Ms. Menendez’s trial until at least July to give her time to undergo a mastectomy and potential radiation treatment after she was diagnosed with breast cancer.

Stephen Gillers, a legal ethics professor at New York University School of Law, noted that Ms. Menendez, in a later trial, could adopt a similar strategy and point a finger of responsibility back at her husband.

“The fact of the two trials enables each to entirely blame the other — perhaps successfully,” Professor Gillers said.

He added that the spouse who is being blamed cannot be forced to address the allegation because of the privilege against self-incrimination as well as a legal doctrine that protects the marital relationship.

In the Menendez case, the success or failure of the senator’s strategy could depend on whether his lawyers can persuade the jury of six men and six women that the once-influential Democrat and former chairman of the Senate Foreign Relations Committee was fooled by his girlfriend-turned-wife.

At the same time, jurors must find that a woman called the shots in such a scheme — a scenario female jurors often accept more readily than some men, according to several defense lawyers.

Rebecca Roiphe, a professor at New York Law School, said she was not so sure that the gender of the Menendez jurors will have much to do with whether his blame-my-wife defense succeeds.

“The stereotype of a woman who’s married to a powerful man and addicted to the trappings of that life and willing to do anything, stop at nothing, in order to get those benefits, that seems like it could go either way,” Professor Roiphe said.

“My guess is it wouldn’t work,” she added. “But all you need is one juror who finds this compelling in order to hang the jury, so maybe they’re hoping for that.”