NEWARK — The bribery trial of Sen. Robert Menendez (D-N.J.) appeared headed for a mistrial after the jury on Thursday said for a second time it could not reach a verdict.

“We cannot reach a unanimous decision,’’ the jury said in a note late Thursday morning. “Nor are we willing to move away from our strong convictions.”

After receiving the note, U.S. District Court Judge William Walls decided to interview the jury foreman privately with the attorneys in the case before deciding the next step.

The jury note did not specify if they were split on all counts. Prosecutors asked the judge to instruct jurors that they could issue a partial verdict on some counts, but the judge declined, saying that would be “going down the slippery slope of coercion.’’

A mistrial would be a temporary victory for the senator and a setback for Justice Department efforts to prosecute alleged public corruption.

After nine weeks of testimony, the jury has struggled to reach a consensus on any of the charges against Menendez and his co-defendant, a wealthy Florida eye doctor.

It’s the second time the jury has said it could not reach a verdict. On Monday afternoon, the jurors first sent a note saying they were deadlocked. The judge sent them home early that day, telling them to come back fresh and try again.

“I realize you are having difficulty reaching a unanimous decision, but that’s not unusual,” Walls told the panel Tuesday morning. He said jurors should decide the case for themselves but shouldn’t hesitate to reexamine their views.

“This is not reality TV, this is real life,” Walls said.

Since the jury has now twice said it is deadlocked, the judge may decide it is time to give them a special instruction called an Allen charge — lawyers sometimes call it a “dynamite charge” — meant to be a final attempt to break a deadlocked jury. Typically such a jury instruction is given after a jury has made clear it is stuck on all counts at a trial. If a jury still insists it is locked even after an Allen charge, a mistrial may be declared.

Menendez attorney Abbe Lowell has argued jurors should not feel “coerced to compromise’’ and has asked the judge repeatedly to declare a mistrial, based on the deadlock notes and other legal and procedural issues.

Faced with 18 separate counts of alleged wrongdoing, including bribery and lying on government financial forms, the panel of seven women and five men seems to be unable to find unanimity on a single count.

If the judge does declare a mistrial, the Justice Department would likely feel significant internal pressure to retry the senator, because recent Supreme Court decisions have raised questions about how much legal authority prosecutors still have in pursuing corruption charges involving payments not explicitly and directly linked to official acts. Some legal experts have warned that a defeat for the government in the Menendez case could lead to a significant scaling back of Justice Department efforts to fight public corruption.

[Supreme Court makes it harder to prosecute corruption]

A guilty verdict, on the other hand, could have had major ramifications in the Senate, where Republicans currently hold a narrow majority. If Menendez had been convicted, there would likely have been pressure on him to resign, or for fellow senators to expel him. If his seat had become vacant before mid-January, New Jersey Gov. Chris Christie would have been able to appoint his successor, likely turning a Democratic seat Republican until a November 2018 midterm election. But it was not clear that even if he had been convicted, whether Menendez and his fellow Democrats would have gone along with his ouster.

Menendez was accused of taking gifts from the eye doctor, Salomon Melgen, such as a luxury hotel stay, private jet flights, and campaign donations, and in exchange intervening in the doctor’s $8.9 million billing dispute with Medicare, assisting with a port security contract of the doctor’s in the Dominican Republic and trying to help Melgen get U.S. visas for his girlfriends.

[Original indictment of Sen. Robert Menendez and Salomon Melgen ]

Melgen is already awaiting sentencing for a previous conviction for defrauding Medicare. The two men were on trial for bribery, and Menendez was also accused of lying on government disclosure forms about his finances when he did not report gifts of flights paid for by Melgen — an omission the senator calls an accidental oversight, not a criminal lie.

Menendez’s lawyers said the government, by charging Menendez, was trying to criminalize a longtime friendship between the two men and that there was nothing corrupt about Menendez’s acts on Melgen’s behalf, or Melgen’s financial support of Menendez.

In closing arguments, Lowell, Menendez’s attorney, said his client’s “deep and abiding friendship’’ with Melgen “destroys every single one of the charges’’ against them.

“Not one document, not one email hints at a corrupt agreement,’’ Lowell told the jury.

Prosecutors countered that the friendship defense raised by the lawyers is no defense at all, because it is still against the law to bribe a friend.

In closing arguments last Monday, prosecutor Peter Koski told the jury that the case was about “a greedy doctor and a corrupt politician” and that Melgen paid Menendez to be “his personal United States senator.”

To try to prove their case, prosecutors called pilots, government officials and even a former senator, Tom Harkin, to the stand to describe how Menendez pushed and prodded officials on behalf of Melgen. At times, those witnesses delivered a mixed message to jurors. Harkin, an Iowa Democrat, said that he had a meeting with Menendez about Melgen’s billing dispute as a “common courtesy’’ among senators — suggesting he didn’t see anything nefarious about the interaction.

The defense spent much of its time putting character witnesses on the stand — including current Sens. Cory Booker (D-N.J.) and Lindsey O. Graham (R-S.C.) — to vouch for Menendez’s character.

The trial has taken place against the backdrop of last year’s Supreme Court ruling that overturned the corruption conviction of former Virginia governor Robert F. McDonnell (R).

Walls tailored his jury instructions to conform to his reading of the McDonnell ruling, which narrowed the definition of an “official act” by a politician.