New Jersey state Sen. Sam Thompson, a Republican, sent a complaint to the Senate Ethics Committee in November calling for an investigation, saying Menendez may have violated Senate ethics by "repeatedly flying on a private jet to the Dominican Republic and other locations ... and soliciting prostitutes." Thompson said he did not hear back from the Ethics Committee.

At an event in Washington on Thursday night, when asked by CNN whether be violated Senate finance rules, Menendez said, "These are nameless, faceless, anonymous allegations. You should find out from them."

The Senate Ethics Committee said it could not comment. Enright said the senator assumes the committee is reviewing the matter, but he has not been contacted.

CNN asked Senate Majority Leader Harry Reid on Thursday whether he thought Menendez was handling the controversy properly.

"First of all, Bob Menendez is my friend," Sen. Reid said. "He is 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."

"I think the issue of the trips alone are probably not enough to suggest that he doesn't have the right to assume the chairmanship of the Foreign Relations Committee," Sloan said. "I think if all the allegations together prove to be true, that would certainly suggest questions about Sen. Menendez's fitness for the chairmanship and perhaps even his position in the Senate."

The executive director for CREW, which sent the Williams e-mails to the FBI, said people should "withhold judgment given the many questions about the source of these allegations and the timing of these allegations. I think the best thing is to wait for the FBI to investigate and figure out what really happened here, if Sen. Menendez did something wrong and if not, who's really behind this effort to smear him."

If this story evolves into a scandal and Menendez is forced to resign, the Democrats' majority in the Senate would likely get one vote thinner. New Jersey law allows Gov. Chris Christie, a Republican, to appoint an interim senator until a special election, which would be no sooner than November.