WASHINGTON — Attorney General nominee William Barr spent nearly nine hours Tuesday answering questions about Robert Mueller's investigation at his Senate confirmation hearing, seeking to assuage Democratic concerns about his views of the Russia probe.

Democrats on the panel spent Tuesday's hearing probing his views on Mueller's investigation into Russian election interference. He faced a barrage of queries about — and criticism of — an unsolicited memo he sent to the Justice Department last year in which he criticized part of Mueller's investigation as "fatally misconceived," as well as questions about his independence from President Donald Trump.

In a terse back-and-forth with Sen. Kamala Harris, D-Calif., a potential 2020 presidential contender, attorney general nominee William Barr said on Tuesday that if he were advised by career ethics officials to recuse himself from the Russia probe and disagreed with that recommendation, he would not heed it.

Harris, referring to Barr's earlier exchanges with her Democratic colleagues on the Senate Judiciary Committee, asked Barr if it would be "appropriate" to go against the advice of Department of Justice ethics officials.

“There are different kinds of recusal,” Barr, 68, responded. "Some are mandated, for example, if you have a financial interest. But there are others that are judgment calls."

"Let's imagine it's a judgment call and the judgment by the career ethics officials in the agency are that you recuse yourself. Under what scenario would you not follow their recommendation?" Harris asked.

“If I disagreed with it,” Barr said.

“And what would the basis of that disagreement be?” Harris said.

"I came to a different judgment," Barr replied.

Sen. Chris Coons, D-Del., also asked at one point, "If you learned the White House was attempting to interfere, would you report that information to the special counsel and to Congress?"

“If I thought something improper was being done, then I would deal with it as attorney general,” Barr said.

Barr defended the memo as having been written in his capacity as a former attorney general — he served previously in the role under President George H.W. Bush — whose legal views are given consideration but for which he possessed no special insight.

"It's very common for me and other former senior officials to weigh in on matters that they think may be ill-advised and may have ramifications down the road," Barr said early on in the hearing. In response to a question from Sen. Dianne Feinstein, D-Calif., the top Democrat on the panel, he said that he was "speculating" when he wrote in the document that Mueller was wrong to probe possible obstruction of justice by Trump.

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In his opening remarks that Mueller’s investigation should continue unimpeded — and that the public should be informed of the results of that probe.

"I believe it is vitally important that the special counsel be allowed to complete his investigation," Barr said.

"I also believe it is very important that the public and Congress be informed of the results of the Special Counsel's work. For that reason, my goal will be to provide as much transparency as I can consistent with the law," he added. "I can assure you that, where judgments are to be made by me, I will make those judgments based solely on the law and will let no personal, political or other improper interests influence my decisions."

Sen. Patrick Leahy, D-Vt. told Barr that some have said that the memo was intended to draw the president's attention to his potential as a possible attorney general.

"That's ludicrous," Barr responded. "If I wanted the job and was going after the job, there are many more direct ways of me bringing myself to the president’s attention than writing an 18-page legal memorandum."

Barr was asked several times about his commitment to making public the results of Mueller's work. In response, he repeatedly said he is committed to making as much information public as he can. But he also suggested that what's made public will not be the Mueller report itself or even a redacted version of it, but rather a summary written by the attorney general.

"I will commit to providing as much information as I can consistent with the regulations," Barr told Sen. Richard Blumenthal, D-Conn., after the Democratic lawmaker asked him to commit to explaining any "changes or deletions" made to Mueller's report to Congress.

Feinstein, meanwhile, told Barr that anyone filling the position of attorney general must be capable of telling the president "no."

"He must have the integrity, the strength and the fortitude to tell the president 'no,' regardless of the consequences," Feinstein said in her opening remarks. "In short, he must be willing to defend the independence of the Justice Department."

Meanwhile, Sen. Lindsey Graham, R-S.C., chairman of the Judiciary Committee, began the opening round of questions with queries about Peter Strzok, Lisa Page, FISA applications, Bruce Ohr and the Steele dossier — all topics of tweets by Trump — as well a recent report that the FBI had opened up a counterintelligence investigation of the president.

"Are you familiar with the January 11 New York Times article about an FBI open inquiry into whether Trump was secretly working on behalf of Russians?" Graham asked. "Can you promise me and this committee to look into this and tell us whether or not — in the appropriate way — a counterintelligence investigation was opened up by someone at the FBI/Department of Justice against President Trump?"

Barr said that he believed "there are a number of investigations" into the matter.

Barr also assured several Democrats he "absolutely” would ensure that Mueller is not terminated without good cause — and that it’s “unimaginable” to think the special counsel would do anything that would cause that to happen.

Asked by Feinstein if the president can order the attorney general to halt a criminal investigation for personal reasons, Barr said, “I think it would be a breach of the president’s duties. It would be an abuse of power.”

Barr also said that he discussed the Mueller probe with Trump “but not in any particular substance,” and volunteered to detail his conversations. Barr added that in June 2017, he was approached by David Friedman, who now serves as ambassador to Israel, about the possibility of personal representation to "augment" Trump’s defense team, but he decided not to pursue the option.

During the hearing, Barr said that he hadn’t researched the emoluments clause, the constitutional provision which forbids government officials from accepting payments and gifts from foreign governments. He also said that he was unfamiliar with the Presidential Records Act, after Sen. Harris asked whether Trump violated the law when he reportedly took the notes from the interpreter during a meeting with Russian President Vladimir Putin in 2017.

Barr on Tuesday also defended the president's goal of building a wall at the U.S. border with Mexico, arguing that it's needed to stop both illegal immigration and the influx of drugs, and said he'd like to see an agreement to end the federal government shutdown.

"I would like to see a deal reached whereby Congress recognizes that it's imperative to have border security," he said. "The point is, we need money right now including barriers and walls and slats and other things."

Sen. Cory Booker, D-N.J., another potential 2020 presidential contender, questioned Barr about his views toward violent crime.

"Do you think that the murders in Chicago...they're related to gangs, gangs involved in drugs," Barr said.

"We can get into the data if you’d like but these are sort of the tropes that makes people believe that in inner cities we should have such profound incarceration rates. I think it’s language like that that makes me concerned and worried," Booker replied.

In his opening remarks and while speaking with Booker, Barr — who has a record of being "tough on crime" — said he was committed to enforcing the First Step Act, the bipartisan criminal justice reform legislation that Trump signed into law late last year, which would ease prison sentences for some non-violent offenders.

Barr, who has been counsel at the Kirkland & Ellis law firm, was attorney general under the first President Bush from 1991 until 1993 after an 18-year civil service career that began at the CIA.

On Wednesday, the committee will hear from experts invited by lawmakers in both parties to speak about Barr. It’s unclear when the panel will hold a vote on his nomination, but it would likely be quickly and the full Senate would likely confirm Barr soon after, which will only require a simple majority vote.