WASHINGTON — When Loretta Lynch is sworn in next week, one challenge will loom larger than the rest: a ticking clock.

As the new U.S. attorney general, who will combat corporate crime and prosecute terrorists, she will have just 21 months to leave her imprint on the Justice Department before her boss, President Barack Obama, steps down.

“She just isn’t going to be around long enough to think in terms of a huge legacy,” said Douglas Berman, a law professor at Ohio State University. “She will likely keep her head down, continue with most of Holder’s policies and make an impact and perhaps shift emphasis where she can.”

Lynch, who was confirmed by the Senate on Thursday, will become the first black woman to serve as the nation’s top law enforcement official, replacing Attorney General Eric Holder. Her confirmation on a 56-43 vote ended a five-month wait over her nomination, which was marked by partisan fights over unrelated legislation and Republican concerns that she won’t be independent enough from Obama.

Holder had more than six years to craft a legacy on issues ranging from civil rights to pursuing terrorists and reforming sentencing laws. Because Lynch agrees with Holder on most issues and faces such a short tenure, she’s likely to make only slight changes to Justice operations.

Lynch, expected to be sworn in on Monday, has offered few clues on how she’ll run the department, and what she has said suggests she’ll essentially be Holder 2.0. She told lawmakers she will focus on deterring and prosecuting cybercriminals and improving relations between police and the communities they serve, two issues already at the heart of the agency’s work.

She will also probably draw more attention to human trafficking and prosecuting white-collar crime, which are also issues that receive significant Justice Department resources. Lynch will likely pick up where Holder left off in making lenders pay for their roles in the subprime mortgage crisis.

When Obama nominated her on Nov. 8, she wasn’t expected to run into much turbulence during confirmation because she wasn’t an ideologue. Instead, she was seen as a tough-on-crime prosecutor who had a compelling personal narrative.

Even so, Republicans said they were skeptical that she would be sufficiently independent from Obama, and they particularly criticized her support for his executive actions on immigration.

Senate Judiciary Committee Chairman Charles Grassley, who voted against her Thursday, said during floor debate on the nomination that he regretted his vote to confirm Holder and that he was opposing Lynch because he’s not convinced she will take the Justice Department in a new direction.

“What we need more than anything else out of our new attorney general is independence,” said Grassley, an Iowa Republican. “The job is not to simply defend the president and his policies.”

Despite that kind of criticism and only winning 10 Republican votes for her confirmation, Lynch has said she wants to establish a better rapport with Congress. Holder had a particularly toxic relationship with Republicans, and in 2012 the House voted to hold him in contempt in a dispute about turning over documents related to a botched operation to track gun-smuggling called Fast and Furious.

Republicans faulted Holder’s oversight of the operation and his responses to lawmakers’ queries about it.