When Attorney General William P. Barr announced a new top federal prosecutor in Brooklyn this month, it was a promotion for one of his closest advisers in Washington.
His choice, Seth D. DuCharme, was not a purely political appointee. Mr. DuCharme spent most of his career in Brooklyn prosecuting terrorists and violent gangs, earning a sterling reputation among many law enforcement officers and defense lawyers.
Still, Mr. DuCharme, 49, is stepping into the position at a fraught time for any U.S. attorney whose office has the jurisdiction to investigate President Trump’s associates. With the election just over three months away, and as political polarization intensifies across the country, Mr. DuCharme is facing scrutiny from all sides.
“Look, I know people have strong views about this administration and folks in D.C.,” Mr. DuCharme said in an interview with The New York Times. “And all I guess I would ask of them is, let’s see how I do.”
Mr. DuCharme seemed keenly aware of the appearances surrounding his promotion. But he said that using the office to advance an inappropriate political agenda would be “inconsistent with every fiber of my being.”
Last month, Mr. Barr and the president ousted Mr. DuCharme’s counterpart in Manhattan, Geoffrey S. Berman, whose office had clashed with the Justice Department over sensitive investigations, including the decision to charge Michael D. Cohen, Mr. Trump’s former personal lawyer.
The current environment demands a delicate dance by U.S. attorneys in high-profile districts. They must get approval from the Justice Department in Washington to charge certain cases while preserving enough independence to maintain credibility with their own rank-and-file prosecutors.
“These are not normal times,” said Daniel Richman, a former federal prosecutor who now teaches at Columbia Law School. “There’s a new risk here that somebody dispatched from Washington, even with his own distinguished personal history, will be seen as some minion of the attorney general.”
Mr. DuCharme’s office, also known as the Eastern District of New York, has jurisdiction that includes Brooklyn, Long Island and Queens. Like its counterpart in Manhattan, the office is pursuing investigations that have touched the president’s associates.
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 negotiating with Goldman Sachs to settle the bank’s role in 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 in 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 in Brooklyn before his 15-month stint in Washington.
“I understand the skepticism, and I’m a flaming liberal, but Seth is 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.
In effect, Mr. Barr arranged for Mr. DuCharme to switch jobs with Richard P. Donoghue, who had served as the U.S. attorney in Brooklyn since January 2018.
As Mr. DuCharme returned to Brooklyn, Mr. Donoghue took Mr. DuCharme’s old place in the Justice Department office that oversees the nation’s federal prosecutors, positioning him to rise should Mr. Trump win re-election.
Earlier this year, the Justice Department assigned Mr. Donoghue to coordinate investigations involving Ukraine — a sensitive role given that federal prosecutors in Manhattan are investigating whether President Trump’s personal lawyer, Rudolph W. Giuliani, broke lobbying laws in his dealings there.
At a congressional hearing on Tuesday, Representative Joe Neguse, a Colorado Democrat, suggested that Mr. Barr had installed Mr. DuCharme as a way to exert more control over those investigations, although it was not clear whether the role would stay in Brooklyn after Mr. Donoghue’s departure.
In Washington, Mr. DuCharme had also served for nine months as a counsel to Mr. Barr and was closely involved in the investigation into the origins of the F.B.I.’s Russia probe, according to emails obtained by the watchdog group American Oversight.
Democrats in Congress have accused Mr. Barr of pursuing the investigation with political motives to justify Mr. Trump’s contention that the F.B.I. had no legitimate reason to investigate his campaign.
Mr. DuCharme was an architect of the Justice Department’s approach to the MS-13 street gang. Last week, the department announced a case that charged an alleged MS-13 leader with a terrorism crime for the first time.
He also advised Mr. Barr not to bring federal charges against a police officer in the 2014 death of Eric Garner in Staten Island. The decision followed a yearslong debate inside the Justice Department under both the Obama and Trump administrations.
Mr. DuCharme grew up in a different Brooklyn — a rural town with the same name in Connecticut. He is a lifelong hunter who hung an elk head from his office wall for many years. He also writes poetry and has performed his work at live venues in New York.
After graduating from Hamilton College, Mr. DuCharme worked as a federal marshal in Brooklyn, chasing fugitives and driving inmates on buses. While he was attending law school at Fordham University, the Sept. 11 attack happened, fueling his desire to become a counterterrorism prosecutor, he said.
At the Eastern District, his signature initiative was a program that offered alternative outcomes for people who could have faced terrorism-related charges. For instance, some defendants were charged with fraud, allowing them to avoid the stigma of a terrorism conviction.
Deirdre von Dornum, the chief federal defender in Brooklyn, recalled one plea deal that Mr. DuCharme had negotiated: He allowed a mentally ill young man who had run at a law enforcement officer with a knife in his pocket to be released into therapy after a year in prison.
“Seth was willing to listen no matter how frightening the facts were,” Ms. von Dornum said. “He really does see every defendant as a person.”
Mr. DuCharme takes over an office where morale has suffered in recent months, partly because of Mr. Donoghue’s heavy-handed reaction to the civil unrest in New York City, according to people familiar with the office.
Last month, Mr. Donoghue brought an indictment that stacked a series of terrorism-related charges against two lawyers accused of firebombing an empty police car so they would face a 45-year mandatory minimum sentence if convicted on all counts.
That decision sparked debate in the office. The supervising prosecutor on the case objected to Mr. Donoghue’s approach and asked to be switched to another role, according to people familiar with the dispute.
Mr. DuCharme has recused himself from the case because his wife, Dyan Finguerra-DuCharme, is a partner at a law firm that employed one of the defendants. Asked if he would have brought the same indictment, Mr. DuCharme responded: “I don’t know. That’s a hard hypothetical to answer.”
Because his tenure may be short — if Joseph R. Biden Jr. defeats Mr. Trump, he could nominate a new slate of U.S. attorneys — Mr. DuCharme said he would focus in the near term on violent crime, given the recent rise in shootings.
“I have no doubt I will disappoint some folks,” he said. “But if you look at where I’ve come from, how long I’ve worked here and the amount of time I’ve had to build empathy with this community, give me a chance.”