Melanie Sloan, the head of a government watchdog group, said Thursday she believes federal investigators are probing Sen. Robert Menendez’s involvement in an alleged travel and prostitution scandal, but predicted that the New Jersey Democrat would not be subjected to internal Senate discipline.

Meanwhile, at a Thursday news conference, Senate Majority Leader Harry Reid, D-Nev., declined to comment on Menendez when pressed by reporters about what he knew about the senator reimbursing a political donor for travel on a private aircraft. Reid encouraged reporters to discuss the matter directly with Menendez.

“Bob Menendez is my friend. He’s an outstanding senator. He is now the new chair of the Foreign Relations Committee. Any questions in this regard, direct to him. I don’t know anything about it,” Reid said.

Menendez did not appear at the news conference with Reid, Majority Whip Richard J. Durbin of Illinois and Sen. Charles E. Schumer of New York, despite the fact that the leaders were speaking about a bipartisan immigration overhaul framework of which the New Jersey Democrat is one of the key negotiators.

Sloan, who runs Citizens for Responsibility and Ethics in Washington, said Thursday that she believes the FBI is investigating Menendez. But, she said it is unlikely that the Senate Ethics Committee will pursue the matter as it stands.

Menendez’s chief of staff, Danny O’Brien, however, said one could assume the ethics panel is investigating the reimbursement issue. He did not offer comment on the prospect of an FBI probe. He said Menendez hasn’t retained a lawyer to deal with any potential fallout.

Last year, Sloan’s group forwarded to the FBI and the Justice Department emails from an source going by the name Peter Williams who indicated that Menendez was linked to a possible scandal involving travel to the Dominican Republic. The matter drew widespread attention Tuesday, when the FBI raided the offices of a Florida doctor, Salomon Melgen, who is a friend of and donor to Menendez.

News reports have said Menendez used aircraft owned by Melgen to travel to the Dominican Republican, possibly to engage in trysts with prostitutes.

Menendez released a statement Wednesday strongly denying the prostitution allegations and acknowledging that he had taken trips on Melgen’s plane, the cost of which he later reimbursed.

Menendez’s staff later explained that the senator had reimbursed him for the flights as recently as this month, even though the trips occurred much earlier. O’Brien said there were no expenditures on the ground at the end of the flights that would be reportable.

Menendez, who won a second full term in November, is not among the wealthiest senators. His personal financial portfolio is worth at least $267,000, according to CQ Roll Call, making him the 285th wealthiest member of Congress.

“Obviously Menendez broke some ethics rules,” Sloan said. “He took some flights that he didn’t disclose as gifts. Now he’s reimbursing personally so he doesn’t have to disclose them.”

Sloan added even if there was an ethics complaint surrounding the matter, the reimbursements “mean they’re done over at Ethics. The worst that could happen is he could get a letter from the Ethics Committee.”

The Senate Ethics Committee has not commented on whether Menendez is under investigation.

Sloan said that as far as the FBI is concerned, “nobody wants to be in the FBI’s sights.”