WASHINGTON (AP) — The Senate Judiciary Committee is poised to approve William Barr's nomination to be attorney general Thursday in a vote that is likely to be mostly along party lines as Democrats have questioned how transparent Barr will be once special counsel Robert Mueller's Russia investigation concludes.

Once the committee approves the nomination, it will head to the full Senate, where Barr is expected to be confirmed. That vote could come as soon as next week.

Barr, who served as attorney general from 1991 to 1993, would replace Attorney General Jeff Sessions, who was pushed out by Trump last year. Acting Attorney General Matthew Whitaker is currently filling the position.

Democrats and many Republicans have said they believe Mueller's final report should be fully released. Barr has said he will be as transparent as possible under Justice Department regulations, but many Democrats are skeptical.

Barr said he takes seriously the department regulations that say Mueller's report should be confidential. Those regulations require only that the report explains the decisions to pursue or to decline prosecutions, which could be as simple as a bullet point list or as fulsome as a report running hundreds of pages.

"I don't know what — at the end of the day, what will be releasable. I don't know what Bob Mueller is writing," Barr said at his hearing last month.

Democrats have also criticized a memo Barr wrote to the Justice Department before his nomination in which he criticized Mueller's investigation for the way it was presumably looking into whether Trump had obstructed justice.

The top Democrat on the Judiciary panel, California Sen. Dianne Feinstein, said last week that she is worried that Barr won't be a check on the president who appointed him.

"This memo is of serious concern to me and appears to be seminal in his appointment to this position," Feinstein said.

Trump had repeatedly criticized Sessions for recusing himself from Mueller's investigation into Russian interference in the 2016 presidential election that includes examining the ties between Russia and the Trump campaign. Trump calls the probe a "witch hunt."

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.

"I don't believe Mr. Mueller would be involved in a witch hunt," Barr said.