WASHINGTON — In his first month in office, Atty. Gen. William Barr has sent a reassuring message to the beleaguered Justice Department — he wants a return to basics after years of disruptive firings, tweet storms and scandals.

In briefings, Barr has asked detailed questions about cases, suspects and legal arguments. He has wandered his fifth-floor hallway to converse about the law.

And he declined the traditional “clap in,” where a newly confirmed attorney general walks through the building and subordinates applaud. Instead, Barr held a three-hour reception in his conference room.

Advisors and associates said the approach reflected Barr’s low-key persona, and his top goals of steering the Justice Department out of the line of political fire, boosting public confidence in it, and improving the morale of its 110,000 employees.

“Everything the attorney general is doing right now is about restoring the [department’s] reputation as a nonpartisan institution whose only allegiance is the law and to the rule of law, not politics,” said J. Michael Luttig, a former federal judge and close friend.

Barr could soon face the toughest test of his tenure. Special counsel Robert S. Mueller III is expected to release his final report in coming weeks, and Barr must decide how much to release to the public.

The pressure on Barr intensified Thursday when the House voted 420 to 0 to demand he release to Congress and the public the full findings of Mueller’s investigation into Russia’s attempts to sway the 2016 election and whether President Trump’s campaign or associates aided the Russians.

“With wide bipartisan support the House has agreed: The American people deserve to know the truth about what, if anything, special counsel Mueller has uncovered, and now we should finally see this investigation come to a close,” Rep. Steve Scalise of Louisiana, the second-ranking Republican, said in a statement.

A White House spokesman, Hogan Gidley, later called the nonbinding resolution “ridiculous,” and it is unlikely to pass the Senate. Sen. Lindsey Graham (R-S.C.), who chairs the Judiciary Committee, blocked a Democratic effort to bring the measure up.

Barr will have to weigh those bipartisan demands against the privacy rights of those not charged with crimes and federal rules governing the release of classified and other sensitive information.

Regulations leave much to Barr’s discretion, and he has been circumspect about his plans, beyond promising to be as transparent as the law allows. Aides said Barr understands the political stakes.

“If he tries to hide the report and evidence, it will not only tar his reputation but also the reputation of the Department of Justice,” said Rep. Adam B. Schiff (D-Burbank), chairman of the House Intelligence Committee. “His decision will have lasting consequences.”

Barr, 68, is hardly a novice. Three decades ago, he served as U.S. attorney general under President George H.W. Bush after previously holding other Justice Department posts. He later served as the top lawyer for two major corporations, GTE and Verizon.

A stalwart of the Republican legal establishment, Barr was in semi-retirement when Trump tapped him in December to again serve as attorney general. He is only the second person in history to hold the post twice.

He has told associates he took the job because the Justice Department faced a critical juncture.

“He reveres the Justice Department as an institution,” said Jonathan Turley, a professor at George Washington University Law School and a friend. “To understand Bill Barr is to understand he has come to the Justice Department with a mission and it is to entirely benefit the institution, not any individuals.”

Barr is particularly concerned that politics may have influenced several high-profile investigations.

Barr was flabbergasted, associates said, at news reports that Peter Strzok, a top FBI agent, and Lisa Page, an FBI lawyer, had exchanged private text messages critical of Trump in 2016 even as they investigated Hillary Clinton’s use of a private email server while she was secretary of State.

Strzok later led the FBI’s inquiry into Russia’s interference in the election and potential links between the Kremlin and the Trump campaign. He was fired last year.

Barr is a proponent of robust presidential authority, and he shares most of the priorities and policy positions of his predecessor, Jeff Sessions, a former U.S. senator from Alabama who had strongly backed Trump’s candidacy in 2016.

But Sessions drew Trump’s ire — and months of demeaning tweets — when he recused himself from overseeing the Russia investigation shortly after he was confirmed. Sessions resigned at Trump’s request in November.

Like Sessions, Barr believes an immigration crisis exists at the southern border, and the Justice Department needs to do more to combat the opioid epidemic and violent crime. Aides say he will lay out his priorities in speeches crafted like legal arguments.

One of his first addresses, they said, will advocate for restricting the ability of federal judges to issue nationwide injunctions halting administration policies.

Judges have blocked the Trump administration from enacting a range of policies, including the initial ban on visitors from several majority Muslim countries and curbing grants to so-called sanctuary cities.

Aides said they expect Barr’s public statements to focus on policy with a markedly different tone than used by Sessions, who was known to wax poetic about the Trump era and the president’s leadership despite their strained relationship.

Barr will advocate for administration policies but is not likely to engage in what some viewed as Sessions’ politicking for the president, according to advisors.

“He supports the president and his policies. He is a conservative,” said a senior Justice Department official who requested anonymity to discuss Barr’s work. “But he isn’t a rah-rah political kind of guy. He thinks and speaks like a litigator.”

Barr starts his office day at 8:30 a.m. when he reviews the president’s daily brief, the intelligence community’s classified, high-level analysis of national security matters. Three days a week, he receives a threat briefing from FBI Director Christopher A. Wray, and he meets every morning with Deputy Atty. Gen. Rod Rosenstein and top aides to suss out issues of the day.

He has gone out of his way in meetings to praise Rosenstein, who has been criticized by Trump. The deputy attorney general is expected to leave office in coming weeks, perhaps after Mueller submits his report.

To improve collaboration, Barr has instituted a weekly “brown bag” lunch in his conference room for top officials. He has spoken to lawmakers of both parties, aides said, and has met daily with a different U.S. attorney to better understand needs and challenges in the department’s 94 districts.

On a recent afternoon, a senior advisor said, Barr popped into Solicitor Gen. Noel Francisco’s office to chat. They soon were engaged in a spirited assessment of an arcane case before the Supreme Court that could result in overturning how courts approach federal agencies’ interpretations of their own regulations.

“He loves the minutiae of the law,” said Turley, the law professor. “He believes the law is found in the details.… If you ask him to read something, he will read every word of it. And he will have questions.”

Times staff writer Jennifer Haberkorn in Washington contributed to this report.