WASHINGTON ― William Barr, the man President Donald Trump has nominated to become the nation’s 85th attorney general, is trying to alleviate concerns about his potential oversight of Robert Mueller’s ongoing special counsel investigation examining Russian interference in the 2016 election. But Democrats are far from convinced that Barr ― who’s been nominated to replace frequent Trump foil and former Attorney General Jeff Sessions ― would protect the Russia probe, and plan to use Barr’s confirmation hearing on Tuesday to extract additional commitments.

Sen. Sheldon Whitehouse (D-R.I.) ― in a letter obtained by HuffPost that the senator hand-delivered to the 68-year-old Barr at a meeting on Thursday ― laid out several lines of questioning ahead of Barr’s appearance before the Senate Judiciary Committee on Tuesday morning. Whitehouse raised a number of questions he had for Barr about his communications with the Trump White House, Justice Department officials, and Trump’s legal team.

Getty William Barr (left), Trump's nominee for attorney general, sent a 19-page memo to Deputy AG Rod Rosenstein in June objecting to Robert Mueller's (right) investigation.

Whitehouse’s letter zeroes in on an unsolicited June 8, 2018 memorandum that Barr sent to Deputy Attorney General Rod Rosenstein, whose anticipated departure has only heightened Democratic concerns about Barr’s appointment. Barr’s 19-page memo suggested that it wasn’t legitimate for Mueller to investigate whether the president obstructed justice by pressuring former FBI Director James Comey to drop the FBI investigation of former Trump national security adviser Michael Flynn.

In the letter, Whitehouse also raised concerns that Trump might want Barr to play the role of Robert Bork, the former solicitor general who ― after Attorney General Elliot Richardson and Deputy Attorney General William Ruckelshaus resigned in protest ― followed President Richard Nixon’s order to fire independent special prosecutor Archibald Cox as he investigated Nixon’s role in Watergate. Whitehouse wrote about an agreement that Bork, then acting attorney general, signed in the wake of what became known as the “Saturday Night Massacre” that offered assurances about the independence of Leon Jaworkski, who replaced Cox as special prosecutor.

“Your agreement to follow in the footsteps of Robert Bork would provide significant assurances to those who fear your appointment is a prelude to another Saturday Night Massacre,” Whitehouse wrote to Barr.

Barr’s confirmation hearing should make for compelling television. The Senate Judiciary Committee, now chaired by frequent Trump defender Sen. Lindsey Graham (R-S.C.), includes several prominent Democrats, including a few who are expected to seek the 2020 Democratic presidential nomination. The hearing is taking place as the nearly 20-month-old Mueller probe enters a pivotal stage, as Mueller appears to be wrapping up his investigation and preparing a highly anticipated report on his conclusions that might jump-start a movement to impeach Trump in the Democratic-controlled House. And it all comes amid an ongoing partial government shutdown, which has left much of the Justice Department Barr hopes to head furloughed or working without pay.

Republicans control the Senate with 53 members, so Democrats can’t do much to stop his confirmation on their own. But they can press Barr for commitments to insure the independence of the Mueller investigation as it enters a crucial timeframe.

Barr, in prepared remarks provided to reporters ahead of Tuesday’s hearing, seemed to be operating under the notion that he would seize control of the Mueller investigation after his confirmation. His prepared opening remarks make no reference to consulting with career ethics officials within DOJ about whether his unsolicited memo about the Mueller probe created an appearance of impropriety that might suggest he should recuse himself from overseeing the Russia investigation. Acting Attorney General Matthew Whitaker, who defended Trump on cable news before joining the Justice Department, rejected the advice of a DOJ ethics official who suggested he should recuse himself from the Mueller investigation. Whitaker, who was not confirmed by the Senate during the Trump administration, had faced questions over the legitimacy of his unprecedented appointment as acting attorney general following Sessions’ forced resignation after the 2018 midterms.

Barr’s opening statement, however, operates on the assumption that he would in fact be in charge of the Mueller investigation upon his confirmation.

“If confirmed, I will not permit partisan politics, personal interests, or any other improper considerations to interfere with this or any other investigation,” Barr will say in his prepared remarks. “I will follow the Special Counsel regulations scrupulously and in good faith, and on my watch, Bob will be allowed to complete his work.”

Barr will also tell senators that he didn’t pursue the position, and that he was “reluctant to be considered” when his name first came up because he’s 68, “partially retired, and nearing the end of a long legal career.” He’ll say that he and his wife were looking forward to spending time with their family, note that he’d already had the gig before, and say he ultimately decided to accept the nomination because he believed in public service.

At least one Democrat on the committee said he thought that Barr’s opening statement offers some reassurances, Sen. Chris Coons (D-Del.) said Monday that Barr set a “good tone” with his prepared remarks before the committee, adding that he “helped himself significantly” by addressing some questions regarding his past criticisms of the Mueller investigation.

The Senate Foreign Relations Committee member added, however, that he still has outstanding concerns about Barr’s views on presidential power, the use of pardons, and his willingness to submit to advice from the department’s ethics officials.

“His last confirmation hearing was 27 years ago ― we can’t pretend that these are similar times. These are very different times and I think its very important he makes his commitment to the rule of law and, in particular, the protection of the investigation led by special counsel Robert Mueller,” Coons said during a conference call with reporters.

Additional reporting by Igor Bobic.