Democrats on the Senate Judiciary Committee are asking the group that governs the legal bar in the District of Columbia to investigate Ed Martin, the interim U.S. attorney in the capital, saying that he had “abused” prosecutorial power by threatening his political opponents.

In a letter to the D.C. Bar’s disciplinary counsel on Thursday, the senators, led by Richard J. Durbin of Illinois, the committee’s top Democrat, also accused Mr. Martin of violating professional standards by refusing to recuse himself from a case involving a Capitol rioter he privately represented and dismissing charges against the man.

Mr. Martin, a Missouri Republican who has used social media to threaten critics of President Trump and Elon Musk, has upended one of the most important U.S. attorney’s offices in the country. He has purged nonpolitical career staff involved in the investigations of the Jan. 6, 2021, attack and at times directly interceded in prosecutorial decision-making.

This week, Mr. Martin took yet another provocative step — sending a letter to the dean of Georgetown University’s law school threatening to investigate the school if it did not scrub its policies and curriculum of diversity and inclusion initiatives, a move made public on Thursday after the Democrats’ letter was sent.

“Mr. Martin has abused his position in several ways,” Mr. Durbin wrote, referring his complaint to the bar group, the body that recommended the disbarment of Rudolph W. Giuliani over false claims he made in lawsuits after the 2020 election.

The D.C. Bar is a mandatory body, to which every lawyer practicing in Washington, D.C., is required to register and which oversees disciplinary actions.

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