It was found that Mr. Gertler used his friendship with Mr. Kabila to act as an intermediary for the mining industry in the Congo. Other companies had to turn to Mr. Gertler to do business with the Congolese state, which cost the country more than $ 1.36 billion in revenue, the finance department said in 2017.

“Gertler is an international businessman and billionaire who amassed his fortune through opaque and corrupt mining and oil deals worth hundreds of millions of dollars in the Democratic Republic of the Congo,” the Treasury Department said in 2018 as it increased sanctions against him .

The application for a new license to allow US companies to do business with Mr. Gertler was processed by the Arnold & Porter law firm. Baruch Weiss, a lawyer for the firm who handled the matter, declined to comment on Sunday, as did Mr Dershowitz.

In October 2018, Mr Gertler hired Mr Dershowitz and Mr Freeh as well as Gregory A. Paw, a former federal prosecutor, to work on the matter. The team then targeted the Treasury Department and the State Department in an attempt to achieve the changes made show lobbying disclosure reports. Also registered in the lobby is Gary Apfel, an attorney who, like Mr. Dershowitz, has been involved in several successful pardons on Mr. Trump in the past few months.

Erich C. Ferrari, an attorney who represents U.S. and overseas corporations on sanctions issues, reviewed the license issued by the Treasury Department on Jan. 15 and said he was surprised at how general U.S. corporations appeared to be allowed to do so to work with Mr. Gertler. despite the sanctions in 2017 and 2018.

“As difficult as it is for me to believe that such a broad license has been granted and exists, I have to say that it is actually a license that directly or indirectly entitles Gertler and companies that own 50 percent or more to with and do business through US banks, ”Ferrari said.

The guard in a statement on Sunday recommended that US banks not unblock Mr. Gertler’s money or “open accounts or otherwise transact for or on behalf of Gertler and his network until this matter is fully investigated and resolved” .

Kenneth P. Vogel contributed to the coverage.