“Your common sense tells you that this is corruption,” he said. “Don’t let the defense overcomplicate your common sense.”

Federal prosecutors say that in exchange for gifts, including private flights and rooms at luxury hotel, as well as campaign contributions, Mr. Menendez, a Democrat from New Jersey, used his office to intervene to try to help a company partially owned by Dr. Melgen gain a lucrative port security contract in the Dominican Republic and came to his friend’s aid when he became embroiled in a billing dispute with Medicare. Both men, who have denied any wrongdoing, are charged with bribery and conspiracy, among other charges.

Mr. Lowell called the charges “a lot of hooey over nothing,” adding that there was “a Grand Canyon” between each accusation and the evidence presented. He said each charge could be innocently explained with one word: “friendship.” He emphasized to jurors that Dr. Melgen’s gifts to Mr. Menendez were, in essence, modest tokens of their close relationship, which began in the early 1990s.

“Gifts solely to cultivate friendship are not bribes,” he said.

Mr. Lowell insisted that Mr. Menendez had never taken any action with the sole intent of benefiting Dr. Melgen. Instead, he said, Mr. Menendez was fighting for issues in the public interest that he had long championed, including making the health care system more equitable and enhancing port security abroad.

“It would help Dr. Melgen perhaps, but it would also do something for the rest of us,” he said, adding that if Mr. Menendez chose to advocate on behalf of legitimate issues raised by a friend, his actions were “legal and proper and appropriate.”