Barr previously served as attorney general from 1991 to 1993 under President George H.W. Bush and is highly respected in the conservative legal world.
Senators debated Barr's candidacy for several hours, focusing on his potential role in supervising special counsel Robert Mueller in the Russian Federation investigation.
In his written testimony to the committee, Barr did write that he believed Mueller was handling the investigation "properly", adding, "My goal will be to provide as much transparency as I can consistent with the law".
A confirmation vote on Barr is expected some time this month. That, combined with Barr's sweeping view of executive power, prompted Leahy to vote no on Barr's nomination. Since then, he's worked as a corporate lawyer in private practice.
In their opposition, Democrats cited a memo Barr wrote past year to Deputy Attorney General Rod Rosenstein before he was nominated objecting to the obstruction aspect of the Mueller probe as "fatally misconceived" and said, "Mueller should not be permitted to demand that the President submit to interrogation about alleged obstruction".
He said Barr did not make such a commitment. After Menendez's case ended in a hung jury, the DOJ declined to re-try him. But he has also noted that he takes seriously department regulations that say the report Mueller submits to the Justice Department should be treated as confidential.
Sen. Richard J. Durbin (D-Ill.) said he felt Barr was a "good person" and likened him to Jim Mattis - Trump's former defense secretary, who had a reputation for being independent and resigned from the administration amid disagreements with the president. Acting Attorney General Matthew Whitaker is now filling the position. "On my watch, Bob will be allowed to finish his work".
The Republican president has repeatedly criticized the investigation as a "witch hunt" and denies any collusion with Moscow.
Barr, the architect behind many tough-on-crime policies that led to disproportionately high rates of incarceration in the African-American community, acknowledged the disparate impacts of those laws and committed to fully enforcing the First Step Act, a piece of landmark criminal justice reform legislation signed into law by Trump in December.