President-elect Donald J. Trump’s announcement that he will nominate Matt Gaetz to be attorney general has resurrected questions about Justice Department and House ethics investigations into Mr. Gaetz’s conduct and whether he had sex with a 17-year-old girl who was being paid for her services.

Here is what we know about the investigations and allegations.

The Justice Department investigated Mr. Gaetz but never charged him.

In 2019, federal authorities in Florida opened a public corruption investigation into one of Mr. Gaetz’s close associates, an Orlando-area local tax collector named Joel Greenberg.

Fashioning himself as a local version of Mr. Trump, Mr. Greenberg was elected to his position in 2016. Shortly thereafter, he began using taxpayer money to buy sports memorabilia, harvest bitcoin and hire cronies, according to federal prosecutors and people familiar with the investigation.

As part of the investigation into Mr. Greenberg, the authorities gained access to Mr. Greenberg’s electronics, revealing that Mr. Greenberg had repeatedly paid young women — whom he met on a website — to attend parties with him and his friends where they used drugs and had sex.

Investigators would ultimately determine that one of the girls who was paid for sex was under 18 at the time.