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By Rebecca Shabad

WASHINGTON — President Donald Trump's nominee to serve as the next attorney general, William Barr, plans to tell Congress this week at his confirmation hearings that special counsel Robert Mueller's investigation of Russian interference in the 2016 campaign should continue unimpeded.

"I believe it is vitally important that the special counsel be allowed to complete his investigation," Barr plans to tell the Senate Judiciary Committee, according to prepared remarks obtained by NBC News.

“For that reason, my goal will be to provide as much transparency as I can consistent with the law,” Barr plans to say. “I can assure you that, where judgments are to be made by me, I will make those judgments based solely on the law and will let no personal, political or other improper interests influence my decisions.”

Trump's vocal dissatisfaction with the Justice Department has sparked questions on Capitol Hill about his plans for the Mueller investigation. Barr is expected to spend two days this week getting grilled by lawmakers about the investigation at his confirmation hearing, which starts Tuesday.

Democrats on the Judiciary Committee — including at least three potential 2020 presidential contenders — have been expected to zero in on a memo Barr wrote last year, in which he criticized Mueller’s investigation into Russian interference in the 2016 election.

Barr sent the document to Deputy Attorney General Rod Rosenstein and another official in the Justice Department who provides legal advice to the executive branch.

“Mueller should not be permitted to demand that the president submit to interrogation about alleged obstruction," he wrote then. "Apart from whether Mueller [has] a strong enough factual basis for doing so, Mueller's obstruction theory is fatally misconceived."

It isn't the only Barr take on executive power or the Russia investigation that has raised eyebrows among congressional Democrats.

Decades ago, when Barr served as President George H.W. Bush's attorney general, he criticized Iran-Contra independent counsel Lawrence Walsh, and was involved in the legal process that led to the pardons of half a dozen officials charged with lying to Congress during the scandal.

Barr told The New York Times in November 2017 that there was nothing “inherently wrong” with Trump’s calls for further investigations into former secretary of state Hillary Clinton, and has said that there are still areas that could be investigated — though he also told The Washington Post the following year that he didn’t think it was appropriate to talk about throwing Clinton in jail or having her prosecuted.

And he has defended other controversial Trump decisions, including the firing of Sally Yates as acting attorney general in January 2017 after she declined to defend the president’s travel ban order in court. “Yates had no authority and no conceivable justification for directing the department’s lawyers not to advocate the president’s position in court,” he wrote in a Washington Post op-ed that year.

But back when he was first selected, Barr's track record — a largely conventional run at the DOJ and top private firms — was considered a top congressional selling point for a Trump appointee.

Barr, 68, who has been counsel at the Kirkland & Ellis law firm, previously served as the nation’s attorney general under President George H.W. Bush from 1991 until 1993 after an 18-year civil service career that began at the CIA.

Now, his statements about presidential power and the Mueller investigation are set to come under heavy scrutiny by Democrats, who have suggested that President Trump nominated Barr to replace Attorney General Jeff Sessions specifically because of those views.

“There’s no reason for a lawyer in private practice to [write a Mueller-critical memo] unless he was attempting to curry favor with President Trump and convey that he would protect the president,” Sen. Dianne Feinstein, D-Calif., ranking member on the Judiciary Committee, said last month soon after his selection.

The document also prompted Senate Minority Leader Chuck Schumer, D-N.Y., to call on Trump as recently as last week to withdraw the nomination, saying that the memo revealed Barr was “fatally conflicted” about being able to oversee the Mueller investigation because he said Barr believes that presidents are “above the law.”

“Mr. Barr has an almost imperial view of the presidency, almost a king, not an elected leader. That much comes across in the memo because it doesn’t allow legal prophecies to work against a president who might be breaking the law,” Schumer said on the Senate floor.

Still, after Sen. Amy Klobuchar, D-Minn., a member of the Judiciary Committee, met with Barr last week, she told reporters that the nominee had said “that he was not going to cut off the Mueller investigation, that he thought it should play out until it was completed.”

“It generally felt like he would allow the report to be issued, but I would clearly want to ask him that under oath,” she said.

Feinstein met with Barr last week and said he gave her a similar assurance, according to The Washington Post.

The new chairman of the Judiciary Committee, Sen. Lindsey Graham, R-S.C., a frequent Trump defender, said that he had also received assurances from Barr that the Mueller probe would remain safe under his watch. Barr, he said, doesn’t believe Mueller is on a "witch hunt," as the president has repeatedly said. Graham also told reporters following his meeting on Capitol Hill with Barr that he and Mueller have been personal friends over more than 20 years, and that their wives participate in a Bible study together.

Sen. Rand Paul, R-Ky., is one of the only Senate Republicans to voice any uneasiness about the pick. In an interview on NBC’s “Meet the Press,” host Chuck Todd said when he heard about Barr’s view on executive power, he thought “uh-oh,” he may have trouble getting Paul’s vote for confirmation.

“'Uh-oh' is right. I'm concerned that he's been a big supporter of the Patriot Act, which lowered the standard for spying on Americans,” said Paul, who isn’t a member of the Judiciary Committee. “I haven't made a decision yet on him. But I can tell you the first things that I've learned about him being for more surveillance of Americans is very, very troubling.”

But Senate Republicans in general have largely praised the nomination, with no signs of any significant GOP potential defections that could threaten his confirmation.

If confirmed, Barr will be only the second person to have the job twice. John Crittenden served twice as attorney general in the 19th century.

If Barr is reported favorably out of committee, his confirmation will require a simple majority in the full Senate — a much easier task with the chamber's new 53-47 GOP majority, and with several Senate Democrats up for re-election in 2020 in predominantly red states.

But first — in the Judiciary panel's first high-level confirmation hearings since Supreme Court nominee Brett Kavanaugh's rocky testimony — he'll face at least two days of tough questions regarding Mueller's job status, the Russia investigation and his views on presidential power.

“I’m concerned when this man, who has a good reputation as a lawyer and professional, volunteers to the Trump administration that they should constrain Mueller’s investigation,” Sen. Dick Durbin, D-Ill., an assistant Democratic leader and Judiciary Committee member, told USA TODAY about the Barr memo. “This is not a good starting point for someone who as attorney general would have supervisory authority over the investigation.”