Joe Biden is expected to give his first public comments over a sexual assault allegation that has roiled his presidential campaign.

The presumptive Democratic nominee for the US presidency will appear on MSNBC’s Morning Joe to address the allegation by his former US senate staff member Tara Reade that he assaulted her in the basement of a Capitol Hill office building in the 1990s.

The former vice president’s campaign issued a statement in early April denying the allegation, and a number of former Biden employees have defended their boss in interviews.

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Mr Biden himself has yet to face any questions or weigh in on the accusation, even as it has taken on fresh attention this week after two of Ms Reade’s associates said she previously told them about elements of her allegations.

Republicans worried about President Donald Trump’s increasingly precarious political standing are seizing on the allegation to portray Democrats as hypocrites who only defend women who allege wrongdoing against conservatives.

They are digging in despite the fact that it could renew attention on the multiple sexual assault allegations lodged against Mr Trump.

Democrats, meanwhile, are in an awkward position of vigorously validating women who come forward with their stories while defending the man who will be their standard-bearer in what many in the party consider the most important election of their lifetimes in the autumn.

Some in the party have been urging Mr Biden to mount a more forceful response to the allegation.

“The campaign has issued statements, but he hasn’t issued any statements in his own voice,” said former Democratic National Committee chairwoman Donna Brazile.

“It’s not helping, it’s just damaging – not only to the person who has come forward, but it’s also damaging the candidate.”

Joe Biden vs TrumpThe former vice president is all but certain to the the Democratic challenger to Donald Trump in the autumn (AP)

Lis Smith, a top strategist on Pete Buttigieg’s presidential campaign, also called on the Biden campaign to speak up.

“These accusations have not been found to be credible, so it’s in the Biden campaign’s interest to nip this in the bud directly and do it quickly,” she said.

The November contest between Mr Biden and Mr Trump will be the first presidential race of the #MeToo era, which has led numerous women to come forward with allegations of sexual assault. Mr Trump has been accused of assault and unwanted touching by numerous women, allegations he denies.

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Women are a core constituency for Democrats, and Mr Biden has a mixed history. While he wrote the Violence Against Women Act as a senator, he also came under heavy criticism for his handling of Anita Hill’s senate testimony in the 1990s.

Just before he launched his 2020 campaign, several women accused him of unwanted touching, behaviour for which he has apologised.

Nancy PelosiUS house speaker Nancy Pelosi (AP)

Mr Biden has pledged to pick a woman as a running mate, and the allegation has left those thought to be in contention in a tough spot.

On Thursday, US house speaker Nancy Pelosi also defended Mr Biden. She told CNN she was “satisfied with how he has responded,” even as she acknowledged “it’s a matter that he has to deal with”.

Republicans have argued that Democrats are not being consistent, pointing to aggressive questioning and coverage of US supreme court nominee Brett Kavanaugh when he faced an allegation of sexual assault.

Speaking about the allegation for the first time on Friday, Mr Trump said Mr Biden “should respond” before proceeding to criticise the treatment of Mr Kavanaugh as “an absolute disgrace to our country”.

Steve Guest, a spokesman for the Republican National Committee, said “the left, and their media allies, has one standard for Republicans and another standard for Democrats like Joe Biden.

“The double standard,” he said, “is appalling.”