The Senate just confirmed William Barr to be President Trump’s new attorney general, a vote that garnered some Democratic support in spite of broader party opposition and ongoing questions regarding his oversight of special counsel Robert Mueller’s investigation into Russian election interference.

Republicans broadly voted in favor of Barr. They were joined by Democrats Doug Jones (AL), Joe Manchin (WV) and Kyrsten Sinema (AZ), all of whom are from states where Trump remains popular.

This is Barr’s second turn as attorney general; he also served during the George H.W. Bush administration, and will again have jurisdiction over a wide-ranging set of issues from immigration enforcement to criminal justice reform to the Mueller investigation. The last of these has been one of the chief sticking points of his confirmation — especially because he has not committed to disclosing the Mueller report in full once it has been completed.

“The defining question for me was his declining to commit to release the Special Counsel’s report fully and completely,” Sen. Richard Blumenthal (D-CT) said in a statement. “He chose not to make the commitment that he would release that report completely and directly to Congress and the American people.”

Democrats pressed Barr numerous times during his confirmation hearing on his reticence to share the entirety of the Mueller report with Congress. He repeatedly said he’d only release “as much information available as [he] can.” As Vox’s Andrew Prokop reported, he also did not agree to follow the guidance of ethics officials if they ask him to recuse himself from oversight of the Mueller investigation.

These responses, along with a memo that Barr sent the Justice Department questioning Mueller’s obstruction of justice case against the president, had many Democrats wondering if he was simply auditioning for the AG job, especially after Trump repeatedly slammed Sessions’s decision to recuse himself from the Russian investigation. In the assurances he did offer, however, Barr said he would enable the Mueller investigation to go on unimpeded and emphasized that it was strongly unlikely that he would fire Mueller.

Deputy Attorney General Rod Rosenstein, who is rumored to be stepping down after Barr’s confirmation, has also said he was confident in Barr’s ability to oversee the probe, and that Barr did not at the time of writing the memo have “the actual facts of the case.”

In the face of overwhelming Democratic pushback, Republicans argued that Barr is exceedingly qualified for the job, and noted that he was unanimously confirmed for the position the last time he was up for a Senate vote in 1991.

Who is William Barr?

Trump nominated William Barr, a conservative lawyer and attorney general under President George H.W. Bush, to be the next attorney general in December. (Barr’s nomination came a month after former Attorney General Jeff Sessions resigned at Trump’s request. Trump initially tapped Sessions’s chief of staff, Matthew Whitaker, to serve as acting attorney general, a questionable appointment whose main qualifications appeared to be defending Trump against the Mueller probe in the press.)

Barr joined the Justice Department’s Office of Legal Counsel in 1989 and rose through the ranks quickly, becoming deputy attorney general in April of that year and then attorney general in 1991 under Bush. Barr served as attorney general from 1991 to 1993, and was one of the youngest people ever to hold the position at the time.

After his tenure, Barr moved into the private sector; he worked as general counsel for Verizon and later joined the firm Kirkland & Ellis. He told associates, according to CNN, that he was willing to come back to the Justice Department out of “a sense of patriotism.”

Given Whitaker’s presence at the Department of Justice, Barr’s nomination was met with some relief: He might be the best-case scenario for a Trump Justice Department appointee. Barr is undoubtedly qualified — he’s a former attorney general, after all — and his past experience meant he likely had knowledge of and respect for the norms and institutions of the DOJ.

Rosenstein, the deputy attorney general who has overseen the Mueller investigation since Sessions recused himself, reportedly greeted the news enthusiastically, as did other DOJ employees.

Barr’s honeymoon phase was somewhat short-lived as his record underwent closer scrutiny. Advocates for immigrants and for criminal justice reform raised red flags about his tenure as attorney general in the 1990s. According to a 1992 Los Angeles Times article, he sought to turn the Justice Department “from a reactive institution” into an “agenda-setting agency,” tackling violent crime, gangs, and tighter immigration controls, among other issues.

Then there’s Barr’s aggressive and expansive view of executive power. Barr, in his past writings, including a July 1989 memo, embraced a strong “unitary executive” view. The doctrine posits that the powers of the executive branch are vested in the president, which means he has full control over executive agencies, and it questions how much Congress can limit or control the president’s executive powers.

There are also questions about how Barr handled presidential investigations in the past. He was involved with some controversial pardons of people involved in the Iran-Contra scandal at the tail end of the Bush administration. Bush, ahead of the 1992 election, wiped away the convictions of six people, including former Reagan Defense Secretary Caspar Weinberger, who had been set to go to trial for lying to Congress. The pardons effectively ended the investigation. Barr, in a 2001 interview, defended those pardons.

Barr’s comments and statements during the Trump era also have some worried about what his appointment might mean for the Mueller investigation. In a 2017 Washington Post article about members of Mueller’s team having donated to Democrats, Barr told the Post he thought it was a sign that the prosecutors might have had a strong party affiliation. “I would have liked to see him have more balance on this group,” he said. Barr wasn’t alone in criticizing the optics of the donations, but others thought it merely played into Trump’s tactics to discredit the probe.

Barr was quoted in a New York Times article last November discussing the president’s call to the Justice Department to investigate Hillary Clinton. When asked what he would do in that situation, Barr indicated that more evidence existed to prompt an investigation into the “Uranium One” deal, a false theory that Clinton sold 20 percent of US uranium stock to Russia, than evidence supporting potential collusion between Trump’s 2016 presidential campaign and the Russians. “To the extent it is not pursuing these matters, the department is abdicating its responsibility,” he said.

Barr also wrote an op-ed in May 2017 defending Trump’s decision to fire FBI Director James Comey. He argued that Comey had erred in his handling of the Clinton investigation during the 2016 election, and he suggested the criticism that Trump fired Comey to interfere with the Russia investigation was unfounded.

These comments troubled lawmakers and others concerned about the integrity of the Mueller probe, and of the Justice Department writ large.

Now that Barr has been confirmed, lawmakers will have an opportunity to see how he ultimately handles this position under entirely new circumstances.