William Barr was sworn in as President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE’s second attorney general on Thursday, putting a new face atop the Justice Department who will assume oversight of special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE’s investigation.

The Senate confirmed Barr in a largely party-line vote amid intense speculation that Mueller’s probe into links between the Trump campaign and Russia is wrapping up.

The investigation — and Barr’s oversight of it — is likely to dominate his first weeks and possibly months as attorney general, depending on when Mueller submits his final report.

Here are five things to watch.

Mueller investigation

Barr, who already served a stint as attorney general in the George H.W. Bush administration, is taking over a sprawling agency with multiple divisions and more than 110,000 employees.

However, Mueller’s investigation is by far the most high-profile issue he will contend with in the immediate term.

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During his confirmation hearing, Barr described it as “vitally important” that Mueller be allowed to complete his investigation and pledged not to allow “partisan politics” to interfere with it. Barr also said he would release as much information about Mueller’s final conclusions as possible consistent with the law — but he was careful not to commit to releasing the report in its entirety.

It remains an open question how Barr’s oversight of the probe will play out. His predecessor, Jeff Sessions Jefferson (Jeff) Beauregard SessionsGOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status MORE, faced tremendous pressure from Trump over the probe, which the president regularly derides as a partisan “witch hunt.”

“His biggest issue is the Mueller probe,” said Seth Waxman, a former federal prosecutor in the D.C. U.S. attorney’s office. “There’s only really two questions he has to answer: One, is he going to interfere, and two, is he going to make the report public?”

Democrats have taken issue with a June memo Barr sent to the Justice Department and White House criticizing Mueller’s inquiry into whether Trump obstructed justice, as well as Barr’s expansive views of presidential power. Some also suggested Barr should recuse himself from the Mueller probe because of his memo.

Republicans, meanwhile, were satisfied by Barr’s comments about the investigation.

“He’s going to err on the side of transparency. I’m not going to take his discretion away from him. I trust him to make a good decision,” Sen. Lindsey Graham Lindsey Olin GrahamSenate GOP aims to confirm Trump court pick by Oct. 29: report The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (R-S.C.), the Judiciary Committee chairman and a close ally of Trump, said recently in Senate floor remarks.

It will be up to Barr whether to release parts or all of Mueller’s report on his findings to Congress or the American public. Any report, legal and national security experts say, will be scrubbed of sensitive national security information and possibly grand jury material.

Leadership shakeup

Barr is expected to make major changes at the Justice Department, beginning with his choice for deputy.

Rod Rosenstein Rod RosensteinDOJ kept investigators from completing probe of Trump ties to Russia: report Five takeaways from final Senate Intel Russia report FBI officials hid copies of Russia probe documents fearing Trump interference: book MORE, who had been overseeing Mueller’s investigation, is expected to depart in the coming weeks after two years on the job. Barr told lawmakers last month that Rosenstein had informed him of those plans and that he had agreed to stay on for the transition.

Various names have been floated as potential candidates for the role, which is subject to Senate confirmation. The New York Times reported that Barr intends to name Jeffrey Rosen, the current deputy secretary of Transportation, to serve as his No. 2.

It is unclear whether Barr will keep on Matthew Whitaker, the controversial figure whom Trump appointed acting attorney general following Sessions’s ouster. Whitaker, a former U.S. attorney in Iowa who worked as Sessions’s chief of staff, quickly emerged as a top target of Democrats as a result of statements he made criticizing Mueller’s investigation before joining the Justice Department.

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Whitaker tangled with House Democrats in a testy hearing earlier this month, during which he defended his decision not to recuse himself from Mueller’s investigation and insisted he had done nothing to interfere with the probe. Whitaker also frustrated lawmakers by refusing to answer various questions about the investigation and his conversations with Trump.

Even if Barr does not decide to keep Whitaker, some say it’s possible he could find a new home in the White House.

“He had to navigate some pretty treacherous waters and he did that very skillfully and if the president is looking for someone else to serve the administration that brings some excellent experience under fire, then I think Matt would be somebody that would fit that description,” said Ian Prior, who worked with Whitaker as a department spokesman under Sessions.

The potential for clashes with Congress

If Whitaker’s appearance before the House Judiciary Committee is any indication, House Democrats are gearing up for contentious hearings with Trump administration officials as they wield new powers in the lower chamber’s majority.

Democrats are almost certain to haul Barr in for a hearing — and soon — to pepper him with questions about the Trump administration’s policies and the Mueller investigation.

House Judiciary Committee Chairman Jerrold Nadler (D-N.Y.), who was critical of Barr’s nomination, announced recently that his committee was hiring former White House lawyer Norm Eisen and white-collar criminal defense attorney Barry Berke as part-time counsels in the panel’s effort to “conduct the sort of oversight that has been completely absent over the last two years.”

Any effort by the Justice Department to withhold details of Mueller’s report — which department regulations state should be confidential and submitted to the attorney general — is sure to spell a fight with Congress, which can subpoena the report if lawmakers so choose.

Barr will also have to answer to the legislative branch on other controversial topics, such as the administration’s immigrant family separation policies, on which Whitaker was grilled earlier this month.

His relationship with Trump

Trump’s public statements about his incoming attorney general have only been positive. During remarks from the White House Rose Garden on Friday, Trump cheered Barr for his “tremendous reputation” and predicted he would do a “great job” as attorney general.

Trump had a notoriously difficult relationship with Sessions, a top Trump campaign surrogate whom the president soured on after the attorney general chose to recuse himself from the Russia investigation.

It’s possible Trump and Barr could also clash over the Russia investigation. Barr notably emphasized his independence from Trump during his confirmation hearing, describing Mueller’s investigation as legitimate and not a “witch hunt” and crediting Sessions for his recusal.

Some doubt, however, that the dynamic will play out the same way.

“It’s going to be very different than, I think, the dynamic between Sessions and Trump because that was early on in an administration that was just getting its sea legs,” said Prior. “I think now everyone is used to the ebb and flow of the Mueller investigation and is well-prepared for its results.”

DOJ, FBI controversies

The Justice Department has faced an onslaught of scrutiny from both parties since the 2016 presidential election.

The department and the FBI have been central to seemingly every controversy, from the investigation into former Secretary of State Hillary Clinton Hillary Diane Rodham ClintonButtigieg stands in as Pence for Harris's debate practice Senate GOP sees early Supreme Court vote as political booster shot Poll: 51 percent of voters want to abolish the electoral college MORE’s emails to former FBI Director James Comey James Brien ComeyDemocrats fear Russia interference could spoil bid to retake Senate Book: FBI sex crimes investigator helped trigger October 2016 public probe of Clinton emails Trump jabs at FBI director over testimony on Russia, antifa MORE’s ouster to the sexual misconduct allegations against Supreme Court Justice Brett Kavanaugh Brett Michael KavanaughOvernight Health Care: US coronavirus deaths hit 200,000 | Ginsburg's death puts future of ObamaCare at risk | Federal panel delays vote on initial COVID-19 vaccine distribution Senate GOP sees early Supreme Court vote as political booster shot Trump says he'll make Supreme Court pick on Saturday MORE.

Trump and his Republican allies have spent the last two years attacking the Justice Department over the Russia probe, alleging that agents engaged in improper behavior in starting the original counterintelligence investigation.

Barr takes the helm of the department at a time when rank-and-file employees are in need of a boost in morale. And it will be up to him to restore trust in Justice and the FBI among lawmakers in Congress in the wake of political controversies.

In a memo to employees Friday, Barr acknowledged that the department has "faced ever-increasing scrutiny from all quarters as news cycles have shrunk from days, to hours, to nanoseconds."

He also described the department as being filled with "talented and dedicated public servants" and pledged to ensure that it enforces laws "evenhandedly, without fear or favor, and — above all else — with the utmost integrity."

Barr is poised to contend with Republicans’ continued allegations of misconduct at the department on the Russia probe. Roughly a year ago, Sessions tapped John Huber, a federal prosecutor in Utah, to investigate Republican allegations of surveillance abuses at the FBI, an inquiry that by all accounts is ongoing.

Last month, Graham asked Barr to promise to look into “what happened in 2016,” citing text messages unearthed by the Justice Department inspector general in which agents criticized Trump before the election. The inspector general ultimately found no evidence that investigative decisions were driven by political motivations.

“Yes, Mr. Chairman,” Barr replied.