The vote was 54-45, primarily on a party-line basis with most Republicans backing President Donald Trump's nominee and most Democrats opposed.

This will be Barr's second tour as attorney general; he led the Justice Department during the George H.W. Bush administration. He takes over a department that Trump has repeatedly criticized for special counsel Robert Mueller's investigation of Russian meddling in the 2016 presidential election.

When Mueller's investigation does wrap up, the decisions around how much information should be disclosed to the public will likely fall to Barr, a noted proponent of strong executive authority.

Barr's deference to the presidency -- he has referred to the role of attorney general as "the President's lawyer" -- is in line with a school of legal thought that draws a vision of uncompromising executive power from the Constitution.

Testifying before the Senate Judiciary Committee last month, Barr refused to commit to release Mueller's final report unchanged, but pledged transparency and said he would put out "as much as I can."

He also said he would not let Trump make corrections to the report before a possible publication, and promised to protect the investigation until its finish.

"I am not going to do anything that I think is wrong, and I will not be bullied into doing anything I think is wrong," Barr said. "By anybody -- whether it be editorial boards, or Congress or the President. I'm going to do what I think is right."

Return to the Justice Department

Barr's nomination last year marked an unusual return to politics for the 68-year-old.

An old guard conservative, Barr has held many of Washington's most influential legal perches, including a stint as the head of the Justice Department's Office of Legal Counsel, where he helped shape legal opinions that influenced White House policy and action.

After Bush's re-election defeat, Barr left government service for lucrative positions in the private sector, becoming the general counsel of Verizon up until 2008 and serving on the board of Time Warner, CNN's former parent company, through last year.

In his confirmation hearing last month, Barr pointed to this distance from the Washington career ladder as one of the reasons he decided to take the job.

"I feel I'm in a position in life where I can do the right thing and not really care about the consequences in the sense that I can truly be independent," Barr said.

Mueller investigation

Barr's claim of independence did little to assuage Senate Democrats skeptical of his potential handling of the looming conclusion of Mueller's investigation.

In their rejection, many Democrats have pointed to a 19-page memo Barr wrote and sent to senior White House and Justice Department officials last year that criticized an element of the special counsel probe.

"We must be clear-eyed about the moment our country is facing and the Attorney General's important role in ensuring the integrity of our democratic institutions," Sen. Chris Coons, a Democrat from Delaware, said in a statement Wednesday announcing his no vote.

Immigration

Barr has a reputation as a hardliner on immigration and crime.

His plans to build a barrier along the US-Mexico border in 1992 will ring familiar in an administration currently engaged in a funding fight for a wall to stop an influx of illegal immigration, and in his confirmation hearing last month, Barr aligned himself with the President's views on border security.

Barr's stance on criminal justice, however, appear to have evolved since he endorsed a Justice Department publication titled "The Case for More Incarceration" in 1992, when violent crime rates hit record highs in the country.

Pressed by Democrats at his confirmation hearing last month, Barr said, "I don't think comparing the policies that were in effect in 1992 to the situation now is really fair," and told senators that he would carry out a newly passed bipartisan sentencing reform bill.

"I think the time was right to take stock and make changes to our penal system based on current experience, so I have no problem with the approach of reforming the sentencing structure and I will faithfully enforce that law," Barr said.

Cybersecurity

Barr will face a new landscape of challenges in his second turn at Justice, including foreign threats and cyber crimes that were not on the department's radar, or even physical possibilities, in the early 1990s.

Chinese state-sponsored hacking and intellectual property theft are now top of mind for the Department of Justice, and federal prosecutors have brought a number of cases against Chinese nationals — and that country's biggest telecommunications manufacturer — in recent months.

"The primary rival of the United States is China. I think Russia is half the size it was when we were facing them at the peak of the Cold War. Their economy's long-term prognosis is nowhere near China's," Barr testified last month.

Barr has also set his sights on American technology companies, and told senators at his confirmation hearing that he would use the Justice Department's antitrust division to explore questions around competition in Silicon Valley.

Barr agreed to return to the Justice Department out of a sense of "patriotism" and he will likely aim to helm the department in a way that restores some normalcy after a period of criticism from the President and his allies, his friends say.

"This is a person who has a special commitment to making sure that the Justice Department is really seen in a great light," said Paul McNulty, a former deputy attorney general who was Barr's top deputy for policy and communications. "He'd really want his legacy on a second time around at DOJ to be that he made the department stronger, because it's that special to him."