After almost three decades of representing Massachusetts in the Senate, Secretary of State John F. Kerry has moved onto to bigger and better things. The former chair of the Senate Foreign Relations Committee, Kerry has left big shoes to fill. His replacement, Senator Robert Menendez, Democrat of New Jersey, does not appear to be up to the task. Upon assuming Kerry’s old job, Menendez was hit by a barrage of ethical misconduct allegations in connection with his relationship to Dr. Salomon E. Melgen, an eye-surgeon who has donated hundreds of thousands of dollars to his campaigns.

Late last month, Dr. Melgen’s offices were raided by the F.B.I. Though the government kept mum about the search, disturbing details soon emerged. Menendez had intervened on Dr. Melgen’s behalf in a dispute with Medicare about billing procedures. In 2010, Dr. Melgen had treated Menendez to free flights to the Dominican Republic aboard his private airplane. Some unsubstantiated reports claimed that while on vacation there the two hired underage prostitutes.

The facts surrounding this case are murky, and no doubt things will come into clearer focus over the next few weeks. The Senate Ethics Committee has begun its own review and Menendez has not been criminally charged. We cannot yet call on him to resign his seat. Nonetheless, the unrecompensed rides, which he finally paid for, represent a severe ethical lapse on their own. The charges also indicate, if not prove, a willingness to place the profit margins of his donors before the national interest. Menendez, for example, may have pushed the U.S. to enforce a Dominican port security plan because it benefit a corporation owned by Dr. Melgen.

Menendez asserts that he has committed no improprieties. He never had sex with prostitutes. He interceded with Medicare to simplify a byzantine reimbursement process. Clerical errors were responsible for the non-disclosure of the plane rides. His involvement in the port security matter was motivated by substantive policy concerns. All this may be true, but how credulous can be we be? A mountain of evidence and an air smacking of “Boardwalk Empire” suggest otherwise.

The Foreign Relations Committee is one of the Senate’s most important bodies. Menendez’s troubles cannot distract from its critical work. Neither should it be led by a man who might monetize the position to detrimental effect. For the duration of the ethics inquiry, Menendez should step down from his post. It wouldn’t be proper to replace John Kerry with a Senator who, if the allegations are true, appears to be only slightly less corrupt than “Boardwalk Empire’s” Walter Edge.