The president’s embattled son, Hunter Biden, is launching an aggressive new legal and public relations strategy, calling on the Office of Congressional Ethics to investigate one of his loudest GOP detractors, Congresswoman Marjorie Taylor Greene. 

It’s one of Mr. Biden’s first public responses to congressional Republicans’ investigation into his tangled business practices and ties to foreign governments.

In a letter obtained by Politico, Mr. Biden’s attorney, Abbe Lowell, said Ms. Greene’s online vitriol is a violation of congressional ethics rules. “Representative Greene’s unethical conduct arises from her continuous verbal attacks, defamatory statements, publication of personal photos and data, and promotion of conspiracy theories about and against Robert Hunter Biden,” Mr. Lowell wrote. 

The letter states that Ms. Greene’s public persona does not “reflect the credibility of the House” as defined in an ethics rule written in the late 1960s. Mr. Lowell points out that a GOP congressman, Matt Gaetz, was admonished by the House Ethics Committee under the same rule he now invokes in 2020 for a social media post that was read to be a threat of retaliation against President Trump’s former personal attorney, Michael Cohen. 

Mr. Lowell provided links to multiple social media posts from Ms. Greene in recent months about Mr. Biden, including when she posted a photo of Mr. Biden and his daughter, referring to the young girl as a “prostitute.”

Ms. Greene took to Twitter on Monday to respond to the letter. “Hunter is upset over my statements,” the Georgia congresswoman wrote. “Well Hunter, the entire country is pissed off about your obvious influence peddling with your Daddy’s political power. Come chat with us Republicans on the Oversight Committee. We have a lot of questions.”

Beyond the congressional inquiry, which is being conducted by the House Oversight Committee, Mr. Biden is also under criminal investigation by federal prosecutors regarding his taxes and whether he lied about his drug use when he bought a gun. 

This new public pugilism from his legal team comes as Mr. Biden recently returned from an official trip to Ireland alongside his father. It marks a turning point, as Mr. Biden has previously kept a low profile during the new Republican majority’s investigation. 

The oversight committee recently claimed that Mr. Biden was involved in a payment scheme that funneled money to his late brother’s widow, who also dated Mr. Biden after his brother’s passing. 

Congressman James Comer, chairman of the House Oversight Committee, says that over the course of three months in 2017, the Biden family collectively received more than $1 million in payments from a business associate of Hunter’s who worked with him in the Chinese energy market, Rob Walker. 

Of that money, Beau Biden’s widow, Hallie Biden, received two payments totaling $35,000 from Mr. Walker’s limited liability companies that the GOP committee says were paid by a Chinese energy company, State Energy HK Limited. It is unclear what business services she provided to receive the money. Hallie Biden used to work as a school counselor, but now sits on the board of the Beau Biden Foundation. 

The committee says Hallie Biden is “a new person of interest in the Biden Business Scheme.”

Mr. Comer says he expects no fewer than 12 Biden family members (including Hunter, Hallie, and Joe’s brother, James) will be eventually exposed in foreign money deals.

“The Oversight Committee is concerned about the national security implications resulting from President Biden’s family receiving millions of dollars from foreign nationals. We will continue to follow the money trail and facts,” the committee said in a statement.