Williams was also cagey when Schwartz pressed for specifics. And his story was shifty—among other things, the number of prostitutes multiplied, and the tipster began alleging that at least one of them was underage. At one point, several women did come forward claiming they had slept with Menendez for money. But they couldn’t offer any proof of their identity, and Schwartz’s team determined that their stories were not credible.

In fact, neither Schwartz nor Sloan found any credible evidence to support the tipster’s allegations. While Sloan suspected the whole thing was a scam, the claims were serious enough that she turned Williams’s emails over to the FBI and asked the bureau to investigate. Based on his email exchange with the agent assigned to the case, which has been uploaded to the Internet, Williams was only slightly more forthcoming with the FBI than he had been with Schwartz.

“The person clearly wanted a scandal rather than an actual investigation,” Sloan says, “because he wouldn’t talk to anyone.”

The scandal did come, albeit slowly. Five days before the 2012 elections, the conservative news site The Daily Caller ran a story under the ham-fisted headline, “Women: Sen. Bob Menendez paid us for sex in the Dominican Republic.” It hinged on the claims of two anonymous women, who also appeared in video with their faces airbrushed out. According to one ABC executive, the women were among those the network had vetted and found less than credible.

The report barely registered with the mainstream media, which was consumed with Hurricane Sandy, but its claims caught the attention of some conservative operatives. As The New York Times reported last month:

In mid-January, after Mr. Menendez was re-elected, someone posted the entire e-mail conversation between Mr. Williams and the F.B.I. agent, Regino E. Chavez, on an Internet site, disclosing to the public that there had been at least an initial inquiry by law enforcement authorities into the matter. Whoever set up this site carefully arranged it so that his or her identity could not be easily traced.

A Republican Party county organization from New Jersey then gave it another nudge, filing an ethics complaint against Mr. Menendez—based on extensive research of flight manifests—that allow it to conclude the senator had improperly flown on Dr. Melgen’s private plane.

[Ken] Boehm, 63, an ex-county prosecutor and a former Capitol Hill aide to Christopher H. Smith, a prominent Republican New Jersey representative, also decided to dive in….He turned up evidence that Mr. Menendez had intervened with officials at the Commerce and State Departments to ask them to help force the government in the Dominican Republic to honor a contract held by a company Dr. Melgen owns to help conduct security inspections at seaports there….

In other words, partisan players investigating the tipster’s dubious claims ended up finding evidence of real ethical breaches. This created a sticky dilemma for reporters, who now had to untangle two overlapping sets of allegations, one of which was more credible than the other.

Those tensions came to the fore on January 29, when the FBI raided Melgen’s South Florida ophthalmology practice as part of a Medicare fraud investigation. The following day, the Herald reported that the FBI was also probing Melgen’s ties to Menendez—including allegations from a “shadowy tipster” that “the two allegedly hired underage prostitutes.” The prostitution claims soon began cropping up in other mainstream outlets. As Washington Post media critic Erik Wemple wrote at the time, it was apparently the FBI probe that “moved the prostitution matter from what Fox News eminence Bill O’Reilly termed ‘lascivious crap’ to what journalists term ‘fair game.’” Wemple also pointed out that an investigation “based on thin and shifty charges” is a flimsy peg to hang a story on.

On the whole, though, the media struck a reasonable balance, at least initially. Many reported in depth on the favors Menendez had allegedly done Melgen, including trying to persuade top federal health officials, who found that Melgen had grossly overbilled Medicare, that the findings were unjust. While some mentioned the prostitution claims, they did so in passing, and they stressed that the claims were dubious. In early February, for example, the Post noted that “the allegations—made by an anonymous whistleblower and first publicized on a conservative Web site—have not been verified independently.”

Those reporters who dug into the evidence found more reason for skepticism. The Miami Herald, which ushered the allegations into the mainstream, dispatched a team of reporters to the Dominican Republican to try to find the alleged prostitutes, based on names and contact information in the tipster’s emails. They turned up “shreds of evidence” that were consistent with Williams’s tale, but “no concrete links” tying Menendez to prostitution. As for the women in question, they were “nowhere to be found.”

Mariah Blake writes for the United States Project, CJR's politics and policy desk. She is based in Washington, DC, and her work has appeared in The Atlantic, The New Republic, Foreign Policy, Salon, The Washington Monthly, and CJR, among other publications.