Barr responded to concerns that the Sessions resignation, the ensuing Matthew Whitaker acting attorney general stint, and Barr's own appointment were all part of an attempt by Trump to frustrate the Mueller investigation.
Whitaker ignored the advice of the career ethics officials who recommended he recuse from overseeing Mueller's probe and reportedly relied instead on the assessment of unknown political advisors.
While it is believed that Mueller will conclude his investigation with a report, the mechanism by which that report will reach the public has been the subject of some concern, particularly with a new Trump nominee, William Barr, preparing to take control of the justice department, including the special counsel's office.
"'As I understand it, his theory is premised on a novel and legally insupportable reading of the law", Barr wrote, the Wall Street Journal reported. Barr has vowed to preserve special counsel Robert Mueller's investigation.
"I also believe it is very important that the public and Congress be informed of the results of the special counsel's work", Barr says.
He described Mueller, a former Justice Department colleague, as a friend he has known personally and professionally for 30 years.
"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 will say, according to the Associated Press, which obtained a copy of his prepared remarks.
Barr will also tell senators that Trump didn't seek any assurances or promises before nominating him. "I can assure you that, where judgments are to be made by me, I will make those judgments based exclusively on the law and will let no personal, political, or other improper interests influence my decision".
Before his nomination to be attorney general, Barr, a longtime Washington DC figure who last held the job during the George HW Bush administration, had emerged as a Trump apologist, defending the firing of Comey in an op-ed and submitting an ostensibly unsolicited memo to the justice department attacking Mueller's investigation of alleged obstruction of justice by Trump as "fatally misconceived".
Russian Federation has denied US intelligence agencies" findings that it meddled in the 2016 campaign, while Trump has denied any collusion with Moscow and called Mueller's probe a "witch hunt'.
"Likewise, President Trump has sought no assurances, promises, or commitments from me of any kind, either express or implied, and I have not given him any, other than that I would run the Department with professionalism and integrity", Barr said. "And, if you confirm me, that is how it will be". He wrote that his memo did not say, "as some have erroneously suggested, that a President can never obstruct justice".
Barr's comments on immigration show similar thinking to former Attorney General Jeff Sessions, who had a hardline immigration policy.