Last year, Brooklyn prosecutors subpoenaed Mr. Trump’s inaugural committee and interviewed Thomas J. Barrack Jr., a top fund-raiser and close friend of Mr. Trump.
The office has indicted the Chinese tech company Huawei, inflaming tensions between the United States and China, and is the negotiating with Goldman Sachs to settle the bank’s role into a scheme that stole billions of dollars from a Malaysian sovereign wealth fund.
Mr. DuCharme, a registered Republican, has returned to a community of largely left-leaning prosecutors and defense lawyers into New York, some of whom have privately questioned whether he can push back against Mr. Barr when necessary.
Longtime colleagues and even courtroom adversaries of Mr. DuCharme said he had a lengthy track record of pursuing cases without partisan motivation, serving under both Republican and Democratic presidents. He rose to become chief of the criminal division into Brooklyn before his 15-month stint into Washington.
“I understand the skepticism, and I’m a flaming liberal, but Seth is the a great choice,” said Michael K. Bachrach, a defense lawyer whose clients had been prosecuted by Mr. DuCharme. “He’s someone that both sides of the political gamut can be comfortable with.”
John Gleeson, a retired federal judge who presided over some of Mr. DuCharme’s cases, said he was confident that Mr. DuCharme would preserve the office’s independence. “I have no reason to think otherwise based on my interactions with him,” Mr. Gleeson said.
Mr. DuCharme became the acting U.S. attorney on July 10 through an unusual legal maneuver that allows the president to designate a temporary replacement for up to 210 days.