Carlson, the editor-in-chief of the Daily Caller, has expressed skepticism ever since the Washington Post reported Monday that Cuban intelligence officers may have planted false allegations that Menendez was involved with underage prostitutes.
In a letter to the Justice Department, Menendez's lawyer contended that the Cuban government had it out for the senator, one of Washington's most vocal critics of the Castro regime.
The Daily Caller published an article on the prostitution allegations in November 2012 after several other outlets passed on the story.
On Wednesday, Carlson pointed to reports by both the New York Times and New York City television station WNBC in which unnamed government officials were quoted as saying there is no evidence to indicate Cuban involvement in the prostitution allegations. Then he called Menendez a liar.
"Let's see: The New York Times and NBC both quoted government sources saying there's no evidence at all that the Cuban government had anything to do with the story," Carlson told TPM in an email. "So Menendez is lying, again. That strikes me as newsworthy."
Tricia Enright, the communications director for Menendez, responded to Carlson's charge with a zinger.
"Who's Tucker Carlson?" she wrote in an email to TPM.
The statement was further than Carlson had been willing to go earlier in the week.
The conservative media honcho had clearly been caught off guard by the Washington Post's reporting when the newspaper interviewed him for its Monday story, calling Menendez's claim "bizarre on its face, but also fascinating."
"I really can't assess it without more information," he said at the time.
In an email to Business Insider that was published early Tuesday morning, Carlson called the claim "bizarre" and "self-serving," while questioning Menendez's credibility.
"I guess this means Menendez no longer thinks the story is part of a racist plot against him, as he initially suggested," Carlson wrote. "But Cuban intelligence? It's a bizarre claim, and self-serving, and they've produced no evidence of any kind to prove it. Obviously we're skeptical, but we're making calls right now to see what we can dig up."
Matt Boyle, the former Daily Caller reporter who first reported on the prostitution allegations, wrote Tuesday on Breitbart News that he was given "no indications" his sources worked for the Cuban government.
Menendez, who is also at the center of a federal corruption investigation, told CNN on Tuesday it made sense the Cuban government would have it out for him.
"The democracy of the people of Cuba -- I have been outspoken in that regard, and I wouldn't be surprised that the regime would do anything it can to stop me from being in a position that ultimately would impede their hopes of getting a different relationship with the United States based upon their interest not the interest of the American people,” he said.
This post has been updated.