Democrats on Wednesday slammed Attorney General William Barr prior to his highly anticipated hearing, with some members calling on him to resign amid revelations that special counsel Robert Mueller objected to Barr's memo on the Russia investigation.

Barr is appearing before the Senate Judiciary Committee , where he's set to face tough questioning about Mueller's letter and subsequent phone call to Barr, complaining that he "did not fully capture the context, nature, and substance" of the special counsel's conclusions.

Sen. Chris Van Hollen, D-Md., reiterated his position on Wednesday that Barr should resign, adding that he "continued to mislead members of Congress."

Van Hollen has taken issue with Barr's answer he gave at an April 20th hearing when the Democratic senator asked the attorney general if Mueller supported the conclusion Barr laid out in his memo. Barr replied, "I don't know whether Mueller supported my conclusion."

"We now know Mueller stated his concerns on March 27th, and that Barr totally misled me, the Congress, and the public. He must resign," Van Hollen tweeted late Tuesday.

In light of Mueller's letter, Barr is defending his 4-page memo, arguing that the special counsel was "very clear [he's] not suggesting we had misrepresented his report."

Before entering the hearing room, Sen. Richard Blumenthal, D-Conn., told reporters that Barr "not only lied to the American people, he lied to Congress." But Blumenthal wouldn't say whether he believes Barr should resign or if he committed perjury, saying he'll wait to hear what transpires in Wednesday's hearing.

"We'll know at the end of the day what the remedy should be, but clearly he lost credibility and I thought he was unfit when he was appointed. But I think now clearly the Department of Justice needs new leadership," Blumenthal said.

"Whether his untruthfulness was illegal, whether he committed perjury, is a fine point that we will debate during the day, but there's no question he mislead the American people."

Sen. John Kennedy, R-La., who's also on the committee, said his main concern is to see whether Barr changed his conclusion on whether President Donald Trump's campaign colluded with Russia or obstructed justice, adding that if the attorney general hasn't "we need to move on."

"He can have an opinion about the summary letter that AG wrote, we all have opinions, I appreciate his opinion but I'm interested in finding out if he's changed," Kennedy said.

"If he's changed his conclusions, he needs to step up and say so. If he hasn't, we need to move on."

Mueller's report concluded that Russia and Trump's campaign didn't conspire in the 2016 election. And while the special counsel couldn't conclude Trump committed a crime, it also didn't exonerate him on obstruction of justice.

Barr is slated to also appear before the House Judiciary Committee on Thursday, but has threatened not to attend because he objects to the format of the hearing. Democrats have planned to have committee attorneys question him. Barr believes he should only answer questions from lawmakers.

