WASHINGTON — Presidential candidate and former Harvard law professor Sen. Elizabeth Warren (D-Mass.) has joined a growing number of Democrats calling on embattled Attorney General William Barr to resign after it was reported late Tuesday that he allegedly misled Democrats in Congress while testifying under oath about Robert Mueller’s findings in the Russia investigation.

“Barr has shamed the office of attorney general with his partisan approach. I think he should resign,” Warren told VICE News on her way to a vote at the Capitol.

Warren is the first sitting lawmaker running for president to call for Barr to go.

“The attorney general does not swear an oath of loyalty to any one individual. The attorney general swears an oath of loyalty to the Constitution of the United States and the people of the United States,” Warren continued. “Barr has made clear that he doesn’t see his loyalty that way, and that disqualifies him from being attorney general.”

Previously only presidential candidate Julián Castro, the former Housing and Urban Development secretary, had called for Barr to step aside, along with just a handful of other Democratic elected officials. But Republicans are brushing aside these calls for the president’s hand-picked attorney general to move on.

“That seems really premature to me,” Senate Majority Whip John Thune (R-S.D.) told VICE News just off the Senate floor. “I think that’s just a knee-jerk reaction.”

Thune and other Republicans were monitoring Barr’s testimony at Wednesday’s Judiciary Committee hearing for any discrepancies, and the attorney general says accusations he misled lawmakers are wrong.

“[Mueller] was very clear with me that he was not suggesting that we had misrepresented his report,” Barr told senators.

Still, that’s not good enough for Democratic leaders who say the emergence of Mueller’s letter to Barr before he previously testified looks pretty damning at first blush.

“I think it is very serious,” House Majority Leader Steny Hoyer replied to a question from VICE News before he began testifying.

But Hoyer and other House Democratic leaders are stopping short of calling for Barr to resign. They’re hoping members of their chamber get to interrogate Barr in person tomorrow, as they’ve requested, though he has resisted their request to have House legal counsel question him as well.

“I think this was not a truthful statement. It’s a very serious thing for the chief law enforcement officer in the country to mislead the Congress about a very salient, key fact,” Hoyer said. “And I think the committee needs to pursue this.”

House Democrats are mulling whether to hold Barr in contempt if he skips Thursday’s hearing in the lower chamber. But they really want him to show up-- after his performance at Wednesday's hearing, they've got a lot more questions for him.