Since then, though, reporters have had time to dig in, and it's become clear that something peculiar was afoot with Menendez's close relationship with a Florida doctor and political donor with whom he traveled twice to the Dominican Republic in 2010. That man, Dr. Salomon Melgen, is now the subject of an FBI investigation, the Miami Herald reports:

Stringing up crime scene tape and using a locksmith, the FBI on Tuesday and Wednesday raided the West Palm Beach business of an eye doctor suspected of providing free trips and even underage Dominican Republic prostitutes to U.S. Sen. Bob Menendez -- who has denied what he calls the "fallacious allegations."

The two men are old friends, the New York Times explains. Their relationship is both personal -- Melgen comforted Menendez when his mother died -- and monetary, with the doctor donating hundreds of thousands to the senator and other Democratic causes. Menendez, in turn, has reportedly used his influence to help Melgen out in business. The senator has now written a $58,000 check to reimburse Melgen for private-plane flights. "We can assume the Senate Ethics Committee is looking at the allegation," Menendez's spokesman said.

But while five-figure reimbursements raise eyebrows, it's the more lurid allegations that make the story more explosive -- and pose the greater political danger. Menendez opened the floodgates to coverage by directly mentioning the prostitution charge in a denial, saying in a statement on Wednesday, "Any allegations of engaging with prostitutes are manufactured by a politically motivated right-wing blog and are false."

Attacking the messenger may typically be a weak strategy, but it's not entirely unwarranted in this case. Boyle, who now works at Breitbart.com, has developed a reputation for juicy, scandalous stories that fall apart on closer inspection -- or sometimes, any inspection at all. He hyped a coup against John Boehner that flopped feebly, claiming to have advance knowledge that at least 17 people would vote against him for speaker (12 did), and in 2011 erroneously claimed that the EPA was planning hire 230,000 new "bureaucrats" -- a fantastic misreading of a Justice Department brief.

Boyle and the Daily Caller both claim to have emails that shed light on the situation. One, reportedly sent by an informant using the name "Peter Williams" to Citizens for Ethics and Responsibility in Washington, includes an email in Spanish that claims to recount Menendez's visits to the Dominican Republic. (Contrary to the DC story, there's no clear indication in the email that any of the women were underage.) And the informant has refused to speak with the FBI by phone or speak on the phone with agents, according to the Herald, complicating the investigation.

This follows closely on another ethical scrape for Menendez. In December, it was revealed that an unpaid intern in his office turned out to be an illegal immigrant who is a registered sex offender. The Department of Homeland Security put an arrest on hold until after the election to avoid the appearance of tampering with politics. And the allegations come as Menendez is set to succeed John Kerry as chair of the presitigious Senate Foreign Relations Committee.