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President Donald Trump's nominee to lead the Department of Justice, William Barr, is scheduled Tuesday to begin the first of two days of confirmation hearings before the Senate Judiciary Committee.

Barr, 68, is expected to defend himself against a barrage of queries from the committee's Democratic minority about his views on special counsel Robert Mueller's investigation of Russia's election meddling and possible collusion with the Trump campaign.

They also plan to grill the conservative Washington insider about his belief in a president's expansive authority, in light of Trump's past threats against Mueller's probe and his more recent flirtation with declaring a national emergency to bypass a negotiating deadlock with congressional Democrats over funding for a border wall. The impasse over funding nine federal departments has led to the longest ever government shutdown.

Barr, who previously served as attorney general in President George H.W. Bush's administration, came under fire from Democrats after it was revealed that he sent a 19-page memo to the DOJ in June, arguing that Mueller's focus on whether Trump had obstructed justice is "fatally misconceived." The memo raised fears among defenders of the Mueller probe that Barr may have been selected because of a bias against the investigation.

Barr's opening remarks will attempt to allay these fears from the outset of the hearings. They appear to show him assuring senators that "it is vitally important" for Mueller to complete his probe, and establishing himself as an independent legal mind who will not be swayed by the president.

Democrats may ask him about possible recusal from any involvement in the probe, similar to his predecessor Jeff Sessions, who recused himself following reports about his contacts with Russia's then-ambassador to the U.S.

Sessions' recusal put oversight duties in the hands of Deputy Attorney General Rod Rosenstein, but could be transferred back to Barr if he is confirmed.

The Democrats on the committee include three potential candidates for president in the 2020 election. Multiple Democrats have already officially announced their campaigns, including former Maryland Rep. John Delaney, or have made major steps toward an official announcement, such as Massachusetts Sen. Elizabeth Warren.

Committee Democratic Sens. Cory Booker of New Jersey, Amy Klobuchar of Minnesota and Kamala Harris of California are all being closely eyed as more Democrats announce their bids to challenge Trump in 2020.

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