Ed Martin was in the mob outside the Capitol on Jan. 6, 2021, posting on social media that the violent riot that day was marked by “faith and joy.”

He has often echoed President Trump’s false claims that the 2020 election was rigged, declaring on the night before the Capitol was stormed that “true Americans” should work until their “last breath” to “stop the steal.”

He has spent the past four years raising money for — and in some cases defending — people charged with joining the mob. And when the House committee that investigated Jan. 6 sent him a subpoena, he never complied, risking criminal charges.

Now, Mr. Martin, 54, has been tapped by Mr. Trump to oversee the U.S. attorney’s office in Washington where he has been put in charge of dismantling the office’s signature project: the sprawling investigation of Jan. 6 that he has energetically opposed.

While his role, for now, is temporary — Mr. Trump has not yet chosen a full-time candidate — Mr. Martin is unlike anyone else who has run the agency that has taken the lead in charging more than 1,500 people in connection with the Capitol attack.

In his long legal career, he has never been a prosecutor, spending more time as a political operative and radio host. Moreover, he is saddled by an array of potential conflicts arising from his efforts to exonerate Jan. 6 defendants — including serving on the board of an organization that helped to pay their legal fees.

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