NEWARK, N.J. — A federal judge on Monday refused to dismiss bribery charges against U.S. Sen. Bob Menendez, ruling that prosecutors had met key legal thresholds defining corruption under a landmark 2016 Supreme Court decision.

The ruling, which came just days after the judge hinted he might toss some of the charges, means the New Jersey Democrat's fate will ultimately be decided by a jury. Attorneys for Menendez and his co-defendant, Florida eye doctor Salomon Melgen, began their defense Monday afternoon.

"There is evidence available to a jury to sustain the determination that the defendant senator sought to exert pressure on or advise other public officials to take official actions for the benefit of Dr. Melgen," U.S. District Judge William H. Walls said, reading his ruling from the bench.

The judge said prosecutors had introduced sufficient evidence to satisfy the Supreme Court's definition of bribery under its ruling last year in McDonnell v. United States. In that case, the high court tossed the conviction of former Virginia Gov. Bob McDonnell and limited what constitutes an "official act."

The high court ruled that a public official cannot be convicted of bribery simply by holding a meeting or setting up a phone call for the benefit of a gift-giver.

Menendez is accused of using the power of his office to advance Melgen's personal and financial interests in exchange for free trips on Melgen's private jet, vacations, and hundreds of thousands of dollars in political contributions.

Prosecutors say the senator worked relentlessly to try to change the outcome of Melgen's $8.9 million billing dispute with Medicare, pressured executive branch officials to resolve Melgen's dispute with the Dominican Republic regarding a port-security contract, and helped obtain visas for the doctor's friends.

Defense attorneys called their first witnesses Monday. Menendez's son, Robert Menendez Jr., testified that Melgen was one of his father's best friends.

Jurors were shown photos of Menendez and Melgen relaxing on lounge chairs at the doctor's home in the Dominican Republic. "He brings out that smile in my dad that's hard to get to sometimes," Menendez Jr. testified, adding that he had traveled with his father to the Dominican Republic on several occasions.

One such time was in 2006, when father and son flew on Melgen's private jet from Florida to the Caribbean nation. Amanda Vaughn, a prosecutor with the Justice Department, asked during cross-examination whether it was true that Menendez Jr. had not taken the jet until his father became a senator.

"That's correct," the younger Menendez said, visibly irritated by the insinuation.

Melgen's wife, Flor Melgen, told jurors through an interpreter that her family had a nickname for the doctor and senator: "SaBob," a combination of their names.

Her son Emilio refers to Menendez as "Uncle Bob," she testified. Flor Melgen said Menendez and her husband were "like brothers."

There was a moment of levity when a defense attorney asked Flor Melgen whether she had a relationship with Menendez independent of her husband's friendship with the senator. "I am married and I am loyal to my husband," she said, prompting laughter throughout the courtroom.

After attorney Kirk Ogrosky rephrased the question, she described Menendez as a friend.

The defense is to continue on Tuesday.

The government rested its case last week. As expected, the defense filed a motion to dismiss the charges, and argued that McDonnell had invalidated the prosecution's "stream of benefits" theory of bribery — that a gift-giver can essentially hold a public official on retainer.

The judge last week expressed skepticism that the prosecution's theory of bribery was tenable under the Supreme Court's McDonnell decision. By Monday, he reached a different conclusion.

Attorneys for Menendez and Melgen wrote in a court filing over the weekend that a number of the bribery charges should be dismissed "because they do not allege, and the evidence adduced at trial did not show, any agreement for Senator Menendez to take specific, identified official acts in exchange for his acceptance of things of value from Dr. Melgen at the time of the alleged quid pro quo."

The judge rejected that argument. That official acts "must be specific and focused under McDonnell in no way imposes a requirement that they be precisely identified at the time the agreement was made," Walls said.

He cited cases in which judges had upheld the stream of benefits theory since McDonnell.

"The government need not prove each gift was intended to prompt" a specific act by the senator, Walls said. Rather, it can demonstrate an illegal quid pro quo "so long as the evidence shows a course of conduct of favors and gifts flowing to the public official in exchange for a pattern of official actions favorable to the donor."