In a potential setback for the government, a federal judge on Friday blocked the introduction of certain evidence that prosecutors wanted to use to support their case that Senator Robert Menendez of New Jersey accepted bribes in exchange for approving billions of dollars in aid to Egypt.

The judge’s order, which comes two weeks into Mr. Menendez’s corruption trial in Manhattan, could undermine prosecutors’ ability to prove certain elements of the multifaceted bribery charges against the senator.

The ruling rests on protections afforded to members of Congress under the Constitution’s “speech or debate” clause, which bars the government from citing specific legislative actions in seeking to prove a federal lawmaker committed a crime.

The U.S. attorney’s office for the Southern District of New York has said it intended to sidestep discussion of official legislative acts and focus instead on promises it says preceded Mr. Menendez’s votes and congressional actions.

The judge, Sidney H. Stein of Federal District Court, ruled in March that although Mr. Menendez’s performance of a legislative act was protected conduct, “his promise to do the same is not.”

The judge’s one-page ruling Friday concerned prosecutors’ proposed exhibits. One set pertained to a message from an Egyptian official to Wael Hana, one of the senator’s co-defendants, asking if it was true that Mr. Menendez was holding up $1 billion of U.S. aid to Egypt.

The other concerned a link to an article reporting on two pending foreign military sales to Egypt totaling about $2.5 billion, which Mr. Menendez’s wife, Nadine Menendez, forwarded to Mr. Hana, writing, “Bob had to sign off on this.”

Judge Stein ruled that the references to prior holds and signoffs would be precluded as evidence against Mr. Menendez.

The senator’s lawyers, Adam Fee and Avi Weitzman, said in a statement that they were “pleased to see the court rein in the prosecutors’ attempts to circumvent the Constitution’s protections for the people’s elected representatives.”

Nicholas Biase, a Southern District spokesman, declined to comment.

Josh Chafetz, a law professor at Georgetown University who studies legislative procedure and the separation of powers, said the “speech or debate” clause “serves the really important purpose of giving members of Congress breathing room to go about doing their business in a way that can’t be interfered with by the executive branch and by the courts.”

In a hearing Tuesday, a prosecutor, Paul M. Monteleoni, acknowledged the challenges posed by the constitutional provision. “The principle that this is designed to make the government’s life harder, to an extent — that applies,” he said.

“But it is also not designed to make members of Congress super citizens immune from all criminal responsibility,” he added.

Ever since the charges against Mr. Menendez, a Democrat, were announced last year, he and his lawyers have argued that prosecutors were seeking to criminalize routine legislative activity.

Mr. Menendez, his wife, Mr. Hana and another New Jersey businessman have all been charged with conspiring to pay bribes to the couple in exchange for the senator’s efforts to meddle with criminal cases in New Jersey, steer aid and weapons to Egypt and to help prop up Mr. Hana’s halal meat monopoly. They have all pleaded not guilty.

Investigators seized more than $480,000 in cash, 13 gold bars and a Mercedes-Benz convertible during a June 2022 search of the couple’s home in Englewood Cliffs, N.J.

Joseph A. Hayden Jr., a criminal defense lawyer in New Jersey, called the ruling a “significant legal victory” that could help to “chip away” at the government’s case.