WASHINGTON — A sexual assault allegation is raising Joe Biden’s first big challenge as the Democrats’ presidential nominee, fueling Republican attacks and leaving many in his own party in an uncomfortable bind.

Biden’s campaign has denied the allegation from his former Senate staffer Tara Reade, who has said Biden assaulted her in the basement of a Capitol Hill office building in the 1990s. But the story garnered fresh attention this week after two of Reade’s associates said she previously told them about elements of her allegations.

Republicans who are 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 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.

The tension is heightened because Biden himself is saying nothing about the allegation.

Like many Americans, he has spent the past several weeks at home to prevent the spread of the coronavirus. He hasn’t held a press briefing since April 2, before multiple news organizations reported Reade’s story. The public appearances he has made, such as fundraisers or events alongside prominent Democrats, have been controlled.

Some Democrats say that approach isn’t working and are urging a more forceful response.

“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.”

Lis Smith, who worked as 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 Biden and Trump will be the first presidential race of the #MeToo era, which has led numerous women to come forward with allegations of sexual assault. Trump himself has been accused of assault and unwanted touching by numerous women, allegations he denies. He was forced to apologize during the 2016 campaign after he was heard on a recording bragging about using his fame to assault women.