The once respectful Democratic primary has devolved into a slugfest about gender, with Hillary Clinton surrogates expressing outrage over how Bernie Sanders is conducting his campaign – even calling for him to fire his staff over alleged sexist remarks.

The ugly dispute has knocked Sanders back on his heels, and placed him on the defensive – an unaccustomed position for a progressive who describes himself as a feminist. And it’s sent a signal flare to Republicans, who have been reminded of the pitfalls of using the wrong language when taking on Clinton – and also of her campaign’s ability to turn it to her advantage.

“I’m stunned that a man like Bernie Sanders, who has clearly committed his life to making the country a better place, would get sucked into this very dangerous rhetoric, which perpetuates sexist and misogynistic stereotypes,” fumed Christine Quinn, the former New York City Council speaker who sits on Clinton’s New York Leadership Council and fundraises for her campaign. “The candidate is supposed to set the tone, set the agenda. If Bernie Sanders does not want to be seen as someone who uses sexist language and perpetuates a dangerous sexist stereotype of strong women, then he should tell his people to stop. And if they don’t stop, he should fire them.”

Quinn, who ran for New York City mayor in 2013, said a recent Bloomberg Politics story that quoted Sanders campaign manager Jeff Weaver joking that “we’re willing to consider her for vice president...we’ll even interview her” was beyond the pale.

“Seriously? Seriously? The absurdity of that statement almost merits no response. How arrogant and sexist can you be? It’s not OK to let people with a long progressive record get away with being sexist.”

Sanders’ predicament has its roots in the first Democratic debate earlier this month, when the Vermont senator said “all the shouting in the world” won’t fix the country’s systemic problem with gun violence -- a comment Clinton and her allies have since interpreted as an implicitly sexist filleting of the former secretary of state.

Sanders insists that wasn’t his intention. But the fight has since escalated, with his top campaign brass (notably, male) blasting Clinton for implying that Sanders’ comment was sexist, and then joking they would consider granting the frontrunner an interview for a vice presidential slot on their ticket.

The episode led Clinton’s allies to publicly leap to her defense, while also quietly predicting the wide gender gap between the candidates will only spread in Clinton’s favor the more she looks like a strong woman under attack by a male opponent.

“The men speaking on behalf of Bernie Sanders should do better,” tweeted Jess McIntosh, communications director for EMILY’s list, a women’s group that is supporting Clinton’s bid. That echoed a statement by EMILY’s List president Stephanie Schriock, who called the commentary “condescending insults by a team who knows better.”

In an interview on MSNBC Thursday, Sanders said some of the statements from his campaign were “inappropriate... clearly I have a lot of respect for Secretary Clinton.”

“If you look at my record in the Congress,” he argued, “you will find there are very few people who have a stronger pro-woman voting record, including a 100 percent record as an abortion rights advocate.” 

Some Clinton allies pointed to the top ranks of Sanders’ campaign as the root of what they see as an insensitivity problem: Sanders’ campaign manager, communications director, field director, early state organizer, Iowa campaign coordinator and top strategists are all men (an aide to the Vermont senator noted that the team’s New Hampshire state director is a woman and Sanders’ chief of staff in the Senate, Michaeleen Crowell, who helps with some campaign duties like debate prep, is also a woman).

“Having diverse perspectives in your campaign leadership results in better strategy, just like having diverse voices at decision making tables results in better policies," said a Clinton ally who declined to criticize Sanders’ team on the record.

The back and forth is taking place against the backdrop of an election where Clinton has highlighted the historic nature of her run since day one, and her campaign has increasingly made its appeal about attracting female voters. On Tuesday evening, the campaign unveiled four new television ads, each 30-second spot telling a story about a specific working woman’s economic plight (Clinton herself did not appear in the ads at all).

On the campaign trail, Clinton has leaned into Sanders’ “shouting” comment.

“I haven’t been shouting, but sometimes when a woman speaks out, some people think it’s shouting,” she said, her voice calm, at the Jefferson-Jackson dinner in Des Moines last weekend, a not-so-subtle dig at Sanders she has weaved into her stump speech since the debate.

An ABC/Washington Post poll released earlier this month -- before the debate or Vice President Joe Biden’s decision to stay out of the race – showed Clinton supported by 61 percent of Democratic women, compared to 22 percent for Sanders. Clinton allies said they expected the war of words over gender would further widen the gap. A Clinton campaign spokeswoman did not respond to a request for comment.

For his part, Sanders has added that his “shouting” remark had nothing to do with Clinton being a woman. “I have been saying for months, well before that debate, that if we are going to go forward on sensible gun reform, people all over this country are going to have to stop shouting at each other,” he said on MSNBC.

Yet the charges of sexism have dredged up accounts of tensions that have simmered in other political races Sanders has run against women – contests where he has fallen into a trap of using careless or insensitive language and argued that his record does the talking for him.

In 1986, when he ran unsuccessfully against Madeleine Kunin for governor, Sanders said gender was not a good enough reason to vote for her.

“Should we vote for [Kunin] because she is a woman? To the degree people think that that’s true, I would regard that as a sexist position,” he said at the time, according “The Socialist Mayor,” a book about Sanders by Steven Soifer.

In an interview with POLITICO, Kunin confirmed the account. “He tried to be more of a feminist than I was to appeal to the women’s vote,” she recalled. 

“I found that very difficult,” said Kunin, the first female governor of Vermont and a former Bill Clinton administration appointee who is now serving as a surrogate for Hillary Clinton’s campaign. “Men can shout and Bernie is a very good shouter. But we’re women. Women raise their voices and it’s considered unseemly. We’re still subconsciously seeing women as different – Bernie should just be careful. To accuse a woman of shouting makes her unattractive.”

Sanders has said he considers himself a feminist based on his record fighting for women’s rights. Yet he ran into trouble in his successful 1985 race for mayor of Burlington, when he faced off against Diane Gallagher. That race also descended into squabbling about gender.

“He is setting me up to the rich bitch, the girl with the pearls, Lady Di,” Gallagher railed, according to a clip from the Burlington Free Press, in which she said Sanders tried to use her gender and wealth to portray her as out of touch with the electorate.

For Clinton, a male rival’s insensitivity has in the past won her political points. A decisive moment in her 2000 Senate election against then-Rep. Rick Lazio came during a debate when he walked over to her with a piece of paper extended and demanded she sign a pledge never to spend soft money in her campaign.

The move was viewed as bullying and aggressive, and ended up being a turning point in the race. Eight years later, Barack Obama managed to avoid any mistakes of that magnitude – though he drew criticism for sounding patronizing when he famously told Clinton in a debate, “You’re likable enough, Hillary.”