Sen. Dianne Feinstein of California, the committee's top Democrat, said that Barr did not commit to providing Mueller's report to Congress, only follow department rules and regulations on what should be public.
Still, the senator said some questions raised over the probe could occupy the committee "for the next decade", and that portions of the final report could be so highly classified that they are never revealed to the public.
Barr said in his hearing last month that he is a friend of Mueller's and that "it is vitally important" that the special counsel be allowed to complete his investigation.
Democrats on the committee said they were concerned that Barr's expansive views of presidential power, as outlined in his memo, would lead him to suppress parts of Mueller's report that address whether Trump tried to obstruct the investigation.
Senators debated Barr's candidacy for hours and focused in particular on the role he will play supervising the Russian Federation investigation led by special counsel Robert Mueller.
"I think we need a new attorney general I appreciate what Mr. Whitaker has done but I think the time has come for new leadership in the department", Committee Chairman Sen.
Sen. Richard Blumenthal, D-Conn., on Thursday said he would vote "no" on Barr's nomination because he has "not committeed to making special counsel findings public and not committed to public testimony from Mueller".
He said Barr did not make such a commitment. "I do not think that any fair-minded person could call Bill Barr a political hack".
Barr pledged at his confirmation hearing to keep politics out of Justice Department decisions and said he would refuse an instruction from the president to fire Mueller absent good cause to do so.
"I hope I'm wrong".
"The American people are entitled to see the facts and judge for themselves", said Louisiana GOP Sen. Durbin said he would vote no.
"Nothing in existing law or regulation prevents the attorney general from sharing the report", Feinstein said before the vote.
Democrats also expressed concern about Barr's memo he sent to the Justice Department past year, unsolicited, that detailed presidential power and said Mueller had a "fatally misconceived" theory that Trump committed a crime when he fired a political appointee, FBI Director James B. Comey, because that was in his powers as president.
All 12 Republicans on the panel voted for Barr, while all 10 Democrats voted against him.
Democrats on the U.S. House of Representatives' Judiciary Committee on Thursday prepared a subpoena to compel Whitaker to testify on Friday, prompting him to say he will not appear unless the subpoena threat is lifted.
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