The Missouri Republican Josh Hawley is wrong to attack Ketanji Brown Jackson, Joe Biden’s supreme court nominee, and should be ignored in confirmation hearings this week, the Senate judiciary chair said.

Hawley, the Illinois Democrat Dick Durbin said, is “part of the fringe within the Republican party … a man who was fist-bumping the murderous mob that descended on the Capitol on 6 January of the last year.

“He doesn’t have the credibility he thinks he does.”

If confirmed, Jackson will be the first Black woman on the court. If Democrats hold their 50 votes she will be installed, via Kamala Harris’s vote as vice-president.

Jackson has attracted Republican support before and some have indicated they may back her this time. Jackson’s confirmation will not affect the balance of a court which conservatives dominate 6-3, as she will replace another liberal, the retiring Stephen Breyer.

Hawley is however one of several hard-right members of the judiciary committee, alongside Ted Cruz of Texas and Tom Cotton of Arkansas, to harbour presidential ambitions. Such senators could see attacking a Biden nominee as a way to appeal to supporters.

This week, in tweets echoed by the Republican National Committee, Hawley highlighted a potential line of attack.

“I’ve noticed an alarming pattern when it comes to Judge Jackson’s treatment of sex offenders, especially those preying on children,” Hawley said.

He did not raise the issue when he questioned Jackson last year, before voting against her confirmation to an appeals court. The White House said the senator was pushing “toxic and weakly presented misinformation”.

Jackson sat on the US Sentencing Commission, an agency meant to reduce disparity in federal prison sentences. The sentencing expert Douglas Berman, an Ohio State law professor, has said her record shows she is skeptical of the range of sentences recommended for child pornography cases, the subject seized upon by Hawley.

“But so too were prosecutors in the majority of her cases and so too are district judges nationwide,” Berman wrote.

Durbin told ABC’s This Week: “As far as Senator Hawley is concerned, here’s the bottom line – he’s wrong. He’s inaccurate and unfair in his analysis.

“Judge Jackson has been scrutinised more than any person I can think of. This is her fourth time before the Senate judiciary committee. In three previous times, she came through with flying colors and bipartisan support, the last time just last year.

“And now Senator Hawley is making these charges that came out of nowhere. The independent fact checkers … have discredited his claims already. They should have. There’s no truth to what he says.

“And he’s part of the fringe within the Republican party. This was a man who was fist-bumping the murderous mob that descended on the Capitol on 6 January of last year. He doesn’t have the credibility he thinks he does.”

This week, Politico demanded Hawley stop using for fundraising purposes a picture of his famous raised-fist salute to protesters before the deadly attack on the Capitol by Trump supporters. Hawley indicated that he would not stop using the image.

On ABC, John Barrasso of Wyoming, a member of Senate Republican leadership, was asked if Hawley was guilty of “character assassination” in his attack on Jackson.

“The whole process is going to be fair, respectful and thorough,” Barrasso said, adding that he found Jackson “clearly, very intelligent”.

Using a key Republican attack line in an election year, Barrasso added: “Going through the record, there are some concerns that people have about her being perceived as soft on crime. That’s all going to come out with the hearings but they’re going to be respectful, they’re going to be thorough and they’re going to be fair.”

Asked if Hawley’s attack was fair, Barrasso said: “Well, he’s going to have his opportunity to question the judge as will all the members of the committee.

“The last time we had a hearing with [Brett] Kavanaugh, he was accused of being a serial rapist with no evidence whatsoever. So, I think we’re going to have a fair process and a respectful process, unlike what the Democrats did to Justice Kavanaugh.”

In fact Kavanaugh – who denied allegations of sexual assault detailed by an alleged victim in confirmation hearings – was the second of three justices installed by Republicans under Donald Trump. The third, Amy Coney Barrett, was jammed on to the court shortly before the 2020 election, after the death of Ruth Bader Ginsberg.

Mitch McConnell, the Republican Senate minority leader, told CBS’s Face the Nation he and Jackson “had a very good conversation”. He asked her, he said, to “defend the court” against those who say Democrats should expand it beyond nine justices to redress its ideological balance.

“Ruth Bader Ginsburg and Justice Breyer both publicly opposed court packing,” McConnell said, “that is trying to increase the number of members in order to get an outcome you like. That would have been an easy thing for [Jackson] to do, to defend the integrity of the court. She wouldn’t do that.”

The man who drastically shifted the balance of the court in part by denying a nomination to Barack Obama in 2016 and swiftly confirmation of Amy Coney Barrett four years later also said: “I haven’t made a final decision as to how I’m gonna vote.”

Hearings begin on Monday. Jackson is expected to make a statement and answer questions. Harvard-trained, she spent two years as a federal public defender. That makes her the first nominee with significant criminal defense experience since Thurgood Marshall, the first Black American on the court.

The American Bar Association has given Jackson its highest rating, unanimously “well qualified”.

Janette McCarthy Wallace, general counsel of the National Association for the Advancement of Colored People, said she was excited to see a Black woman on the verge of a seat.

“Representation matters,” Wallace said. “It’s critical to have diverse experience on the bench. It should reflect the rich cultural diversity of this country.”

• The Associated Press contributed to this report