After the U.S. attorney in Manhattan announced corruption charges last Friday against Senator Robert Menendez of New Jersey, the veteran Democratic lawmaker lashed back, calling the claims false and saying prosecutors had “misrepresented the normal work of congressional office.”

Mr. Menendez has said a lot more in recent days about the indictment, but his assertion last week offered a clue to the defense he may invoke, if his case goes to trial, one that other public officials facing corruption charges have used successfully.

In a series of key rulings since 2010, the U.S. Supreme Court has repeatedly narrowed the legal definition of corruption, leading to overturned convictions of prominent politicians in New York and elsewhere.

In 2016, in throwing out the conviction of Bob McDonnell, a former Republican governor of Virginia, the court said a quid-pro-quo scheme had to encompass more than routine courtesies like arranging meetings — the normal work Mr. Menendez invoked.

But investigators found gold bars and cash-stuffed envelopes in Mr. Menendez’s home, and several legal experts interviewed this week said they believed the charges in the 39-page indictment could withstand the kinds of legal challenges that defense lawyers have successfully used in the past.

“It’s true that the Supreme Court keeps narrowing the scope of what is permissible for the government to pursue,” said Rachel E. Barkow, a professor of criminal law at New York University. “But I do think that this case falls into the heartland of what’s always been permissible, because as I read it, this is classic bribery.”

Daniel C. Richman, a professor at Columbia Law School, said, “The Supreme Court’s point has always been not to criminalize normal politics” — what he called “the regular constituent service and day-to-day work of legislators.”

“Obviously, there have to be some limits to normal constituent service — and perhaps bars of gold will help draw that line,” Mr. Richman added.

But David Oscar Markus, a Miami trial lawyer who has read the indictment, cautioned against the rush to judgment of many of Mr. Menendez’s critics, who he said have simply accepted the government’s version.

“They’re willing to convict him without ever hearing from the defense,” said Mr. Markus, who represented Andrew Gillum, a former Democratic governor candidate in Florida who faced a trial in which he was acquitted of lying to the F.B.I. The jury failed to reach a verdict on 18 other counts, which were later dismissed.

“The first thing that I think is important for any criminal defense lawyer to do is not to take anything in that indictment as true or at face value, and to question every single paragraph,” Mr. Markus said.

The indictment charges that Mr. Menendez, 69, who as chairman of the Senate Foreign Relations Committee held sway over military sales, financing and other aid, secretly took hundreds of thousands of dollars in bribes, including gold bullion, in return for helping the government of Egypt.

The government also charged the senator’s wife, Nadine Menendez, and three New Jersey businessmen. One, Wael Hana, is an Egyptian American who prosecutors say maintained close connections with Egyptian military and intelligence officials, and was a linchpin in the scheme that funneled the money to the senator and his wife.

Mr. Menendez, his wife, and the three other defendants all pleaded not guilty this week.

Mr. Hana, a longtime friend of Ms. Menendez, had founded a business that had little revenue in 2018 and early 2019; in the spring of 2019, the Egyptian government designated it as the sole certifier of halal meat that was exported to that country, despite Mr. Hana’s lack of experience with halal certification.

One day after an Egyptian official told Mr. Hana that his firm was likely to become Egypt’s only halal certifier, Ms. Menendez texted her husband: “Seems like halal went through. It might be a fantastic 2019 all the way around.”

The indictment says Mr. Hana’s monopoly assured “a revenue stream” from which he could “make good on the bribe payments” he had promised the Menendezes.

It says that in exchange for Mr. Menendez and his wife’s promise that he would use his authority to facilitate military sales to Egypt, Mr. Hana promised to put Ms. Menendez on the payroll of his company in a job where she would do little or no work.

In one 2018 episode, Mr. Menendez agreed, at his wife’s request, to ghostwrite a letter lobbying other U.S. senators to release a hold on $300 million in aid to Egypt. Mr. Menendez then emailed the draft to his wife, who forwarded it to Mr. Hana, who then sent it to Egyptian officials. Two months later, Mr. Menendez texted his wife, asking her to tell Mr. Hana that he would sign off on a $99 million military deal.

The indictment says that U.S. Department of Agriculture officials contacted the Egyptian government in 2019 asking that it reconsider its grant of monopoly rights to Mr. Hana’s company, IS EG Halal. Mr. Menendez called a high-ranking department official and insisted “the U.S.D.A. stop opposing IS EG Halal’s status as sole halal certifier,” according to the indictment.

Randall D. Eliason, a former federal prosecutor who teaches white-collar criminal law at George Washington University, said that on its face, the indictment presents “a pretty damning case” in its accounts of meetings and the passing of information to Egypt and payments to Mr. Menendez and his wife from their co-defendants.

But, he said, the indictment seems “a little unclear” on what payments Mr. Menendez was receiving, and when, in return for specific actions he was taking.

“That’s going to be the key: Can you link it up and prove the quid pro quo — that he took a particular action because of a particular gift?”

Professor Eliason noted that in an earlier corruption trial of Mr. Menendez that ended in a hung jury in 2017, the government showed the senator received gifts but failed to convince the jury that he agreed to exercise the power of his office in exchange.

Alexandra Shapiro, a lawyer who has represented a series of clients in public corruption appeals, said the issue of whether Mr. Menendez exchanged official acts for bribes will be a question for the jury.

“It will likely depend on what inferences the jury can draw from the timing of the alleged bribes and any official action he took,” said Ms. Shapiro, of the firm Shapiro Arato Bach.

Arlo Devlin-Brown, who from 2014 to 2016 served as chief of the Southern District’s public corruption unit and today is a defense lawyer at the firm Covington & Burling, said he believed that if proven, Mr. Menendez’s pressuring of the Agriculture Department official in order to protect Mr. Hana’s monopoly very likely satisfies the Supreme Court’s definition of an official act.

He said the defense may ask the judge, Sidney H. Stein, to dismiss or narrow the indictment because many of the allegations do not amount to official acts under the Supreme Court’s latest interpretations. He, too, said the judge may leave such questions for a jury to decide, based on the government’s evidence.

Mr. Devlin-Brown said that given the Supreme Court’s tighter definition of corruption, the Southern District may be more conservative in the legal theories it charges and the jury instructions it seeks.

But, he added, “I think public corruption continues to be a significant priority for the U.S. attorney’s office for the Southern District of New York, and I don’t see that changing any time soon.”