Representative Matt Gaetz, Republican of Florida and a close ally of former President Donald J. Trump, is being investigated by the Justice Department over whether he had a sexual relationship with a 17-year-old and paid for her to travel with him, according to three people briefed on the matter.

Investigators are examining whether Mr. Gaetz violated federal sex trafficking laws, the people said. A variety of federal statutes make it illegal to induce someone under 18 to travel over state lines to engage in sex in exchange for money or something of value. The Justice Department regularly prosecutes such cases, and offenders often receive severe sentences.

... Matt Gaetz claims that Nestor is his adopted son. There are no adoption papers to support this claim, and Nestor has a whole-ass father who is alive and well and hasn’t given his son up for adoption. Yet, no one has truly questioned the nature of this adoptive relationship that doesn’t include an actual adoption.

In August, federal investigators added charges that Greenberg had used his government position to commit identity theft and accused him of sex trafficking a child.

Investigators said they found several fake IDs inside Greenberg’s home, and accused the tax collector of improperly accessing a state database to access personal information of people he was in “sugar daddy” relationships with, including a minor victim between the ages of 14 and 17. Greenberg allegedly made the fake IDs to help “facilitate his efforts to engage in commercial sex acts,” according to the indictment.

On Tuesday, the case against Greenberg, 36, gained national prominence after the New York Times reported that it had also sparked a separate criminal probe into allegations that Gaetz had sex with a teenage girl.