Sen Bob Menendez, a Democrat, went on trial in Manhattan federal court Monday, accused of accepting bribes of gold and cash to use his influence to deliver favors that would help three New Jersey businessmen. Menendez, 70, sat with his lawyers and listened as Judge Sidney H. Stein told two separate groups of 50 prospective jurors about the charges against Menendez and two of the businessmen. The judge told them the “sitting U.S. senator from the state of New Jersey” had been charged in a conspiracy in which he allegedly “agreed to accept bribes and accepted bribes.” After he warned them that t…