William Barr confirmation hearing - LIVE: Trump's attorney general nominee grilled by Senate over Mueller investigation

Ms Feinstein says there on ongoing concerns about the memo Mr Barr wrote to the Justice Department last year that was critical of Mr Mueller’s view of obstruction of justice and his robust view of executive power.

"Do you have the strength and commitment to defend the independence of the Justice Department?" Ms Feinstein asks in her opening statement.

Sen. Orrin Hatch began his remarks by saying it was a pleasure to introduce William Barr, saying “I have known and worked with Bill closely over the years and am glad to call him a friend.”

He called him an “outstanding choice” and a “defender of the rule of law.”

“He has shown his commitment to the Constitution time and time again while serving the country. That's why he's been confirmed unanimously by the Senate three times," Mr Hatch continued. 

William Barr has been sworn into the hearing, introducing his family in his opening statement. 

Here’s William Barr’s opening remarks: 

“It is a privilege to come before you today. I am honored that President Trump has nominated me for the position of Attorney General.”

"I regret that I come before this Committee at a time when much of our government is shut down. My thoughts today are with the dedicated men and women of the Department of Justice, and other federal workers, many of whom continue to perform their critical jobs.”

William Barr admits he was not looking to serve again, saying he was “half-retired” but noted “I believe I can do a good job leading the department in these times.” 

Barr served as attorney general from 1991-1993.

William Barr says he and Robert Mueller are friends and that he “has confidence he will handle the matter properly.” 

"Given his public actions to date, I expect that the Special Counsel is well along in his investigation. At the same time, the President has been steadfast that he was not involved in any collusion with Russian interference in the election," he said. "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 added “that the public and Congress be informed of the results of the Special Counsel’s work.”

William Barr has addressed the controversial unsolicited memo he sent to the Justice Department last year criticising Robert Mueller’s probe into Donald Trump’s alleged obstruction of justice. 

"The memo did not address – or in any way question – the Special Counsel’s core investigation into Russian interference in the 2016 election. Nor did it address other potential obstruction-of-justice theories or argue, as some have erroneously suggested, that a President can never obstruct justice. I wrote it myself, on my own initiative, without assistance, and based solely on public information," he said. 

William Barr has outlined his immigration views, saying “As a Nation, we have the most liberal and expansive immigration laws in the world.”

"We attempt to take in huge numbers equitably from all around the world. Legal immigration has historically been a huge benefit for our country. But most of the world’s population lives well below our own poverty level, and we cannot possibly accommodate the many millions more who would want to come here if we had no restrictions,” he continued.

William Barr has finished his opening statements. Here's his conclusion:

"If confirmed, I will give priority to protecting the integrity of elections. I will build on the work already done by Special Counsel Mueller and current Department of Justice leadership and ensure that the full might of our resources are brought to bear against foreign persons who unlawfully interfere in our elections. I believe that our country must respond to any foreign interference with the strongest measures, and we must work with partners at the state level to ensure that our election infrastructure is completely protected. Fostering confidence in the outcome of elections also means ensuring that the right to vote is fully protected, as well as ensuring the integrity of elections."