Joe Biden, discussing sexual assault claims in early 2018, told PBS flatly, “Women should be believed.” On Friday, facing his own accusations, he stressed on ­MSNBC the importance of “taking the woman’s claims seriously when she steps forward — and then vet it, look into it.”

That shift in Biden’s tone reflects the way a former staffer’s claim that he assaulted her 27 years ago is raising new questions for the #MeToo movement. Democrats and women’s activists, eager to unseat a president they consider deeply misogynistic, are facing tough decisions over whether to stick by Biden or distance themselves — and whether to redefine what emerged as a stark rallying cry after centuries of injustice: “Believe women.”

Among those publicly wrestling with such issues is Alyssa Milano, an actress, #MeToo activist and Biden supporter. “How do progressive women choose between the p---y grabber in chief who has done so much damage to our country and a man who has allegations made against him?” Milano wrote in Deadline, which covers Hollywood and entertainment.

She added, “Believing women was never about ‘Believe all women no matter what they say,’ it was about changing the culture of NOT believing women by default.”

Some longtime women’s rights activists warn that downplaying former staffer Tara Reade’s claims could undermine the movement’s credibility by suggesting it only targets men whose policies it dislikes.

“I think that this could potentially signal the end of MeToo,” said Michele Dauber, a Stanford University law professor who heads the Enough is Enough Voter Project and has called for an investigation. “The failure to investigate, and the failure to live by our principles, will become silencing.”

Republicans have wasted little time accusing Democrats of hypocrisy, citing their near-uniform outrage when sexual assault allegations arose in 2018 against Supreme Court nominee Brett M. Kavanaugh — which, like those against Biden, involved long-ago events and notable but limited corroboration.

Reade has accused Biden of sexually assaulting her in 1993 in a semiprivate area of the U.S. Capitol complex. Reade says Biden pinned her against a wall, reached under her skirt and pushed his fingers inside her. She was a 29-year-old staff assistant at the time.

The accusation received some corroboration in recent days when Business Insider published an account by a former neighbor who said Reade told her about the alleged incident several years after she said it occurred. The neighbor, Lynda LaCasse, confirmed that account to The Washington Post.

Biden’s appearance Friday on MSNBC’s “Morning Joe” was the first time he had personally addressed Reade’s claim, and it came as a growing number of women’s groups and activists were urging him to do so.

“It is not true,” Biden said of the allegations. “I’m saying unequivocally it never, never happened, and it didn’t. It never happened.”

Asked to comment for this article, Biden’s campaign pointed to remarks from the candidate’s fundraiser Friday night denying the accusation but adding that it is appropriate for Reade’s claims to be investigated. “It isn’t enough just to simply take my word for it and to dismiss it out of hand,” Biden said during the virtual event. “Frankly, that shouldn’t be enough for anyone, because we know that this sort of approach is exactly how the culture of abuse has been allowed to fester for so long.”

From the beginning, many #MeToo activists emphasized that while accusers should be taken seriously and treated respectfully, that did not mean they should be believed without question. During the furor over Kavanaugh, for example, many of his critics supported one of his accusers, psychology professor Christine Blasey Ford, while remaining wary of others.

“Believing survivors is about a paradigm shift away from assuming that survivors are lying right out of the gate, which has been our cultural and societal norm,” said Shaunna Thomas, co-founder of UltraViolet, a group that advocates for gender equality.

Even so, the Biden allegations are prompting a struggle for many activists.

“Two things can be true,” said Rebecca Katz, a liberal Democratic operative. “There may be allegations that are credible, and also that Joe Biden might make a much better president than Donald Trump. And it is a real struggle trying to confront that.” She added, “If you’re going to say that you believe women, then you need to believe women.”

Even Lynda LaCasse, the former neighbor who provided some corroboration for Reade by saying Reade told her about the alleged incident several years after she said it happened, voiced ambivalence after seeing Biden’s MSNBC appearance.

“He looks very believable, too,” LaCasse said Friday in an interview with Democracy Now!, an independent news program. “But I’m hearing this today, and I heard Tara a long time ago telling me that. So, I’m struggling with it, with the election now.” She still intends to vote for Biden, she said.

Reade’s accusation is the latest in a string of sexual misconduct allegations against powerful politicians in recent years. Women’s advocates acknowledge the responses have shifted over time, because of the specific circumstances as well as an evolving political landscape.

An early explosive charge came in 2017, when Republican Senate candidate Roy Moore of Alabama was accused of sexual misconduct involving young women, including one teenager who said he molested her. Leaders from both parties — with the exception of President Trump — abandoned Moore, and a Democrat was elected to the Senate from the deep-red state.

Moore denied the allegations, calling them “completely false” and “a desperate political attack by the National Democrat Party and the Washington Post,” which broke the story. He also filed a defamation lawsuit against his accusers.

Around the same time, multiple women said they had been groped by Sen. Al Franken (D-Minn.), who resigned in January 2018 after condemnation from both parties. Franken denied the allegations, and some Democratic leaders later said they regretted their role in his ouster because he had not received a fair process, while many other figures stood by their calls for him to resign.

The response was more divided later that year when Kavanaugh faced accusations of sexual assault dating back to his high school years, which he passionately and at times tearfully denied. Republicans largely backed him, while Democrats lined up behind Ford.

A Quinnipiac University poll taken after Ford and Kavanaugh both testified in the Senate showed 86 percent of Democrats believed Ford’s allegations, while 84 percent of Republicans accepted Kavanaugh’s denials.

There was also a gender gap, with women more likely than men to believe Ford, by 55 to 40 percent. Younger voters were more accepting of her account as well, with 57 percent of those under 35 saying they believed her. Ultimately Kavanaugh was confirmed by the Senate in a 50-to-48 vote almost entirely along party lines.

Now the Biden episode appears to be opening a new phase of the #MeToo movement. Women’s rights activists passionately want to unseat Trump, who has repeatedly spoken of women in vulgar terms, disparaged their looks and been accused of assault by more than a dozen women.

Trump has denied the assault allegations, sometimes by denigrating the accusers; after writer E. Jean Carroll accused him of attacking her in a clothing store dressing room, Trump fired back that “she’s not my type.” After The Post obtained a 2005 video of Trump boasting that “when you’re a star” women let you do anything including “grab them by the p---y,” Trump apologized, but also dismissed it as locker room talk.

Complicating the already fraught issue, a number of sensational claims of sexual assault have been discredited in recent years.

In 2015, Rolling Stone retracted an article that vividly described an alleged gang rape at a University of Virginia fraternity house. The magazine also settled two defamation cases related to the piece, paying millions of dollars to a college administrator and a fraternity mentioned in the article. Nearly a decade earlier, in 2006, three Duke University lacrosse players were wrongly accused of raping a stripper, another case that attracted national attention.

The current tempest comes at a striking moment in the history of women in politics.

Many women reacted to Trump’s ascent with a surge of impassioned activism, leading the “Resistance” movement and electing dozens of female Democrats to the House in 2018. A protest march in Washington the day after Trump’s inauguration attracted more than 1 million women from across the country wearing pink hats.

Biden himself has just emerged from a Democratic presidential primary field that included several prominent women for the first time, including four U.S. senators. In part to address the disappointment among activists that none of them prevailed, Biden has promised to choose a female running mate and pledged to name the first black woman to the U.S. Supreme Court.

Biden has not been publicly accused of sexual assault in his long public career by anyone other than Reade, but he has faced complaints of insensitivity. His conduct at the confirmation hearings of Justice Clarence Thomas in 1991 was condemned by many liberals for his treatment of Anita Hill, and more recently some women have said he embraced or touched them in unwelcome ways.

On policy, Biden is praised by women’s activists for championing the Violence Against Women Act, a cause he has cited several times in recent days, including at an event this week with Hillary Clinton.

None of the women on Biden’s short list to be his running mate has publicly voiced discomfort about the Reade allegation, including Sens. Amy Klobuchar (D-Minn.) and Kamala D. Harris (D-Calif.), whose pointed interrogations of Kavanaugh raised their profile and helped fuel their own presidential bids.

Sen. Kirsten Gillibrand (D-N.Y.), an outspoken supporter of the #MeToo movement and one of the strongest voices for ousting Franken, said this week that women need to be heard in these situations and backed Biden saying, “Vice President Biden has vehemently denied these allegations, and I support Vice President Biden.”

On Thursday, House Speaker Nancy Pelosi (D-Calif.) sought to balance her support for #MeToo and Biden.

“I want to remove all doubt in anyone’s mind — I have great comfort level with the situation as I see it, with all the respect in the world for any woman who comes forward, with all the highest regard for Joe Biden,” Pelosi said at her weekly news conference.

Before Biden’s MSNBC appearance, The Post contacted all four members of “The Squad,” freshmen women in Congress who have bucked Democratic leadership on other issues and were outspoken in their condemnation of Kavanaugh. None responded or provided a comment.

Ana Navarro-Cárdenas, an anti-Trump Republican who is on the board of directors for Time’s Up, an organization to combat sexual harassment and assault, pointed to a balance sheet of sorts that compares Trump’s response to Biden’s.

“Every accused, whether president of the United States or president of the Hair Club For Men, should be held accountable and expected to directly respond to the allegations with seriousness and transparency,” she said in an email. “Joe Biden did just that with his one and only accuser, though he should have done it sooner. Donald Trump has yet to do that with his dozens of accusers. Given what we know today, it’s Joe Biden by a mile, for me.”

It is not the first time women’s activists have grappled with assault allegations against a politician whose agenda they embrace. In the early 1990s, numerous allegations emerged against then-Sen. Robert Packwood (R-Ore.), a champion of women’s rights, and some women’s groups later admitted they were slow to forcefully condemn his behavior.

Former president Bill Clinton also faced allegations of sexual harassment and assault, and some activists now concede they were insufficiently supportive of those women and too slow to condemn Clinton. The women involved include Monica Lewinsky, the White House intern who had an affair with Clinton, and others who accused him of sexual assault or harassment in his pre-presidential years.

Amid the varied responses to Reade’s allegations, a small number of #MeToo activists have sharply condemned Biden, including for his silence before the television interview.

“Answer your taxpayers, answer Tara Reade, stop speaking through your manager,” said Rose McGowan, an actress whose accusations helped bring down Hollywood mogul Harvey Weinstein. “You are a creep. You know it. We know it. I know it. Tara definitely knows it.”

But Tarana Burke, the activist who coined the term MeToo, offered a more typical response.

“The inconvenient truth is that this story is impacting us differently because it hits at the heart of one of the most important elections of our lifetime,” she said in a social media post. “And I hate to disappoint you but I don’t really have easy answers.”