William Barr, President Donald Trump’s nominee for attorney general, spoke before the Senate Judiciary Committee on Tuesday in the first of two sessions, making his case that he’s qualified to replace the fired Jeff Sessions.

Barr is no stranger to confirmation hearings, having served as attorney general from 1991 to 1993 under former President George H. W. Bush. But the 68-year-old will faced tough questions about his past views of special counsel Robert Mueller’s investigation into Russia’s meddling during the 2016 election, which he will oversee if he’s confirmed.

During his opening remarks, Barr assured senators that he thinks Mueller should be permitted to finish his investigation.

“I believe it is in the best interest of everyone — the president, Congress, and, most importantly, the American people — that this matter be resolved by allowing the special counsel to complete his work,” Barr said.

Barr was forced to answer questions about an unsolicited memo he sent to the Justice Department last year criticizing Mueller’s inquiry into potential obstruction of justice by Trump, which Barr characterized as “fatally misconceived.” Barr told senators he would not fire or interfere in Mueller’s investigation without good cause, even if Trump ordered him to do so.

“I would not carry out that instruction," Barr said.

Here are the highlights from the hearing:

Barr: I won’t go after marijuana companies

Barr told senators that he would not go after companies that sell pot in states that have legalized either medical or recreational marijuana.

During his tenure as attorney general, Sessions rescinded the Cole Memo, an Obama-era guidance that prevented the federal government from going after companies or individuals in states that have passed marijuana laws.

"My approach would be not to upset settled expectations,” Barr said. “Investments have been made, so there has been reliance. However, I think current situation is untenable. It’s almost like a backdoor nullification of federal law.”

Pennsylvania, New Jersey, and Delaware have all legalized the sale of marijuana for medical reasons.

Barr added that he supports a federal pot ban, telling New Jersey Sen. Cory Booker, “I think it’s a mistake to back off on marijuana.”

Barr says he would not fire Mueller without good cause

Barr told senators that he would not fire Mueller without good cause, even if Trump ordered him to do so.

“Assuming there was no good cause?” Barr said, “I would not carry out that instruction.”

Barr added that he would resign rather than do something he felt was unlawful, a position he thinks every government official should share.

Barr says Rosenstein is sticking around

Barr told senators he has no plan to oust Deputy Attorney General Rod Rosenstein if he is confirmed. In fact, Barr said he had asked Rosenstein to stay in his role during the transition from acting Attorney General Matthew Whitaker.

“Rod and I have been talking about his plans. He told me he viewed it as a two-year stint,” Barr said. “I asked him to stay for a while, and he said he would… He has no concrete plans, I have no concrete plans in terms of his departure. We’re going to sort-of play it by ear.”

Multiple news outlets reported last week that Rosenstein was expected to leave his post after Barr’s confirmation.

Barr backs Trump’s proposed border wall

During a second round of questions that began shortly after 12:30 p.m., Barr told senators that he backs the president proposal for a wall along the U.S.-Mexico border.

"I feel it is a critical part of border security that we need to have barriers on the border. We need a barrier system on the border to get control,” Barr said. “Part of that is illegal immigration but a big part of it is preventing the influx of drugs."

Barr also echoed Trump’s own comments on the need to change immigration laws, and said he’s “inclined to support” a Republican bill that would punish undocumented immigrants who have committed a crime.

Barr: I won’t be ‘bullied’ by Trump or anyone

Trump has attacked the Justice Department repeatedly during his first two years in office. So Democratic Sen. Dick Durbin asked Barr the obvious question: Why does he even want the job?

"Well, because I love the department and all its components, including the FBI. I think they are critical institutions that are essential to preserving the rule of law, which is the heart beat of this country,” Barr said. “And I feel that I'm in a position in life where I can provide the leadership necessary to protect the Independence and the reputation of the department and serve in this administration."

Barr also told Durbin his age and experience running the Justice Department make it easier to stand up to anyone who might try to coerce him into changing is views, whether it be a newspaper editorial or the president himself.

“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. “I’m going to do what I think is right."

Barr won’t commit to following the advice of ethics officials

Sen. Patrick Leahy (D., Vt.) asked Barr if he would recuse himself from handling Mueller’s investigation if ethics officials determined there could be a conflict due to his past statements about the Russia probe.

“I will seek the advice of the career ethics personnel, but under the regulations, I make the decision as the head of the agency as to my own recusal,” Barr said. “I would certainly consult with them, and at the end of the day I would make a decision in good faith based on the laws and the facts that are evident at that time.”

Trump repeatedly criticized Sessions for making the decision to recuse himself, tweeting on several occasions that Sessions “should stop” Mueller’s investigation.

“Jeff Sessions should be ashamed of himself for allowing this total HOAX to get started in the first place!” Trump wrote on Twitter in December.

Barr admits talking about Mueller’s investigation with members of the White House

Barr admitted to Feinstein that he spoke about Mueller’s investigation with members of the White House, but said it was “not in any particular substance.” Barr offered to go into more details about the people and content of those conversations, but Feinstein declined, as her time had concluded.

Barr also denied reports that Trump wanted to add him to his legal team, saying he had just once conversation with the president in 2017.

“That’s the only time I met him before I talked to him about the job of attorney general, which is obviously not the same as representing him,” Barr said.

Barr: ‘I don’t believe Mr. Mueller would be involved in a witch-hunt’

Faced with questions about Mueller by Graham, Barr said he considered the current special counsel a “good friend” who was fair-minded and had his trust to run an unbiased investigation.

“I don’t believe Mr. Mueller would be involved in a witch-hunt,” Barr said.

Trump has repeatedly called Mueller’s investigation a “witch hunt,” and has attempted to undermine the investigation’s public creditability.

Barr agreed with Graham that Sessions was correct to recuse himself from overseeing Mueller’s investigation (something Trump repeatedly chastised) and praised current deputy attorney general Rod Rosenstein.

Barr also promised Graham he would look into anti-Trump text messages exchanged between former FBI agent Peter Strzok and former FBI lawyer Lisa Page, saying he was “shocked” when he saw them.

Feinstein asks Barr if he has ‘strength’ to stand up to Trump

During her opening remarks, ranking member Dianne Feinstein (D., Calif.) questioned whether Barr had the strength to stand up to Trump, pointing out the president’s repeated calls to investigate his political rivals, such as former secretary of state Hillary Clinton.

“Do you have that strength and commitment to be independent of the White House pressures that you will undoubtedly face?” Feinstein asked rhetorically. “Will you protect the integrity of the Justice Department above all else?”

Watch: Live video of the hearing