Roger J. Stone Jr., the longtime associate of President Trump’s, has been lobbying for a pioneering cryptocurrency investor known as “Bitcoin Jesus” who is facing federal fraud and criminal tax charges, according to congressional filings.

Mr. Stone filed paperwork last month indicating that he had been retained by Roger Ver, an early Bitcoin investor who was charged last year and accused of shielding his cryptocurrency holdings from $48 million in taxes.

Mr. Stone noted in a filing last week that he had been paid $600,000 by Mr. Ver since early February to help his client’s case, partly by trying to abolish the tax provisions at the heart of the charges.

Mr. Ver, a former California resident who renounced his U.S. citizenship in 2014, was arrested last year in Spain, according to the Justice Department, which announced plans at the time to extradite him.

Mr. Ver disputed the charges, claiming in a video posted on social media in January that he was being threatened with a possible sentence of more than 100 years in prison because of his political views and his role in promoting cryptocurrency.

In the video, which was framed as an appeal to Mr. Trump, Mr. Ver linked his case to the president’s grievances about the weaponization of the justice system.