WASHINGTON (Reuters) - The U.S. Senate confirmed William Barr as attorney general on Thursday, installing a seasoned lawyer with decades of Washington experience to head the Justice Department and putting him in charge of overseeing Special Counsel Robert Mueller’s long-running probe of whether President Donald Trump’s 2016 campaign colluded with Russia.

FILE PHOTO: William Barr smiles during a break in his Senate Judiciary Committee hearing on his nomination to be attorney general of the United States on Capitol Hill in Washington, U.S., January 15, 2019. REUTERS/Yuri Gripas/File Photo

The Senate voted 54 to 45, largely along party lines. A Justice Department spokeswoman said Barr will be sworn in at 4:45 PM ET in the Oval Office of the White House by Chief Justice John Roberts.

Many Democrats opposed Barr out of concern he might not make Mueller’s findings fully public. But the Senate is controlled by Trump’s fellow Republicans, so Barr’s confirmation was virtually assured.

“Today is a great day for the Department of Justice with the confirmation of William Barr to be the next Attorney General,” said Senate Judiciary Committee Chairman Lindsey Graham.

“He is a steady hand at a time of turmoil and he will bring much-needed reform to the Department of Justice.”

Previously attorney general from 1991 to 1993 under President George H.W. Bush, Barr has won praise from lawmakers in both parties for his expertise and grasp of the workings of the Justice Department.

He would be the third man in barely two years to occupy that post, replacing acting Attorney General Matthew Whitaker, who replaced Attorney General Jeff Sessions. Trump ousted Sessions last November after criticizing him repeatedly.

Mueller is investigating meddling by Russia in the 2016 U.S. presidential election and whether Moscow colluded with Trump’s campaign to try to tilt the election in Trump’s favor, as well as possible obstruction of justice.

Trump denies any collusion. The Kremlin denies any meddling.

Before being nominated, Barr wrote a 19-page legal memo, in which he called part of Mueller’s probe into whether the president obstructed justice “fatally flawed.” He shared it with Trump’s legal team and Justice Department officials.

Barr has said he will not let himself be bullied by Trump and will protect the integrity of Mueller’s investigation and make public as many of its findings as he can.

Barr has not promised to release Mueller’s report in its entirety. He has warned he may not be allowed to reveal the identities of people who escape prosecution. That stance troubles many Democrats, who say Barr’s expansive views of executive power might lead him to suppress parts of the report.

“The Justice Department needs a leader who will be independent of the White House and who is able to stand up to President Trump,” said Senator Dianne Feinstein, the top Democrat on the Senate Judiciary Committee, in a statement.

“Bill Barr hasn’t demonstrated that he would be that independent leader.”

Despite Democrats’ opposition, many were anxious to have Barr installed quickly so he would replace Whitaker, whose tenure has been fraught with controversy since Trump appointed him in November.

Critics have alleged Whitaker’s appointment was unlawful. Democrats fear Trump installed Whitaker to undermine Mueller’s probe because Whitaker had criticized it when he was a conservative pundit.

Barr is widely expected to back many of Trump’s tough immigration policies. He will also be under the microscope for how he implements a new law that eases prison sentences for non-violent criminals, after he advocated for the opposite, tough-on-crime approach for decades.