“We have to grapple with the fact that some people think a woman can’t win … I have heard about it from our own people [and] I’ve noticed it,” Klobuchar told POLITICO in an interview. The Minnesota Democrat called it “a real barrier” that’s only grown more obvious as the primary has ground on. It has prompted her to speak more openly about sexism, she said, “especially because I’ve seen my very qualified sisters have to leave the race — that was really, for me, a turning point.”

But Klobuchar and Warren have addressed sexism is markedly different ways. In debates and on the campaign trail, Klobuchar for months has addressed it head on. Warren, by contrast, has mostly been mute on the subject — until Tuesday night’s debate.

Both strategies contain risks and highlight the headwinds all female candidates face. Claiming sexism or addressing it publicly can obscure a candidate’s broader message and quickly earn accusations of playing the so-called “gender card,” according to aides and allies to both candidates and officials from past presidential campaigns of women candidates. But ignoring it or brushing it off can let damaging gendered narratives take root and spread, they said.

Joe Biden himself recently acknowledged the double standard some female candidates face, but as part of an argument for his own electability. “I think there's a lot of sexism in the way they went after Hillary. I think it was unfair. An awful lot of it. Well, that’s not gonna happen with me,” he said at a campaign stop in Iowa this month.

Warren, who’s filtered her campaign message largely through a class-based lens, has declined to call out sexism when pressed by reporters, though her campaign and its surrogates have addressed it more directly. When prodded by a reporter last fall over Biden casting her as “angry” and “condescending,” and whether he would have made those comments about man, Warren shot back: “Why don’t you ask him that?” And unlike many of the men in the race, Warren has been more reluctant to go negative against opponents .

“Many times when women point out contrasts with other candidates they’re savaged for that compared to when guys do it,” said former presidential candidate Julián Castro, who endorsed Warren last week.

Warren did address the issue explicitly in the debate Tuesday, however, after reports this week that Bernie Sanders told Warren in a private meeting in 2018 that a woman couldn’t beat Trump. Warren confirmed that account of the meeting, but Sanders denied it.

“This question about whether or not a woman can be president has been raised, and it’s time for us to attack it head-on,” Warren said on stage. “Can a woman beat Donald Trump? Look at the men on this stage. Collectively, they’ve lost 10 elections. The only people on this stage who have won every single election that they’ve been in are the women — Amy and me.”

After the debate, Sanders and Warren confronted each other on stage. "I think you called me a liar on national TV," Warren alleged. After a brief back and forth, Sanders said: "You called me a liar."

“I do believe the electability question has been used as a weapon against these women,” said Christina Reynolds, who served as deputy communications director for Hillary Clinton in 2016.

The balance was tricky for Warren. She was careful not to call Sanders himself sexist, and her campaign privately urged its supporters to follow her lead.

“I think it’s true individual candidates have done sexist things, often unwittingly,” said Brian Fallon, Clinton’s press secretary in 2016. “But calling out individuals as sexist is more prone to have people ignore the bigger thing they’re pointing out and saying, ‘Oh, that’s divisive.’”

Klobuchar has been more willing to call out “double standards” for women in the primary. In recent weeks she’s ramped up her criticism of a system that’s never elected a woman president, though Clinton did handily win the popular vote. Klobuchar often ties it to her own pitch on electability: her record of winning statewide in Minnesota, a swing state where she’s drawn support deep into Trump counties.

On Sunday night, she reminded more than 100 voters gathered here during a snowstorm that while Democrats “better not screw this up.” But she added, “If you don’t think a woman can beat Donald Trump, Nancy Pelosi does it every single day,” a line she had previously deployed in a debate.

“I never intended to, nor am I running on it, running on, ‘Oh, elect a woman.’ … When Obama was going to be the first African American president, he did not [play up] that very much,” Klobuchar said. “[But] as you can see by some of these numbers in polls, what people are hearing on the ground, I still think it’s a major factor. And sometimes I think people aren’t really even realizing it in their head, and I think they need to grapple with it and we need to make the case.”

Still, there are risks for both candidates because “you don't want to be seen as the candidate who is complaining, which complicates how you can call out sexism,” said Ian Sams, the national press secretary for Kamala Harris’ presidential campaign. “Walking that fine line — identifying it without being seen as playing the victim card — is very hard to do, and what they’re dealing with now.”

Warren and Klobuchar’s differences in strategy also signal their positions in the primary.

“Amy Klobuchar is playing a hot hand right now as she’s trying to get into that top tier, but she has nothing to lose. Elizabeth Warren sat at the top of this for a very long time, and when you’re at the top, you’re very cautious,” said Sue Dvorsky, a former Iowa Democratic Party chairwoman who initially endorsed Harris. “They’re just in different places in the race, and that explains some of their differences in willingness to address it until this point.”

Though a debate over sexism burst through the primary this week, it’s been a persistent force that’s shaped the Democratic primary since its earliest days, aides for several campaigns acknowledged. Biden described Warren as “angry” in a Medium post in October and MSNBC commentator Donny Deutsch chastised her for a “high school principal demeanour,” both seen as sexist tropes. Amy Klobuchar’s campaign launch in February was consumed by headlines about her treatment of staff, which her defenders believed wouldn’t have been levied against or portrayed in the same way with a tough male boss.

At Kirsten Gillibrand’s first news conference as a presidential candidate, she was asked about her likability. During a Fox News town hall, she was chastised for being impolite. And last spring, Harris, who faced the challenge of running as a black woman, had to defuse rumors that she’d become Biden’s running mate. A whisper campaign about the No. 2 role circled around Harris even though she was running for the top job herself, shaping perceptions of her candidacy.

“The women candidates are waging a concurrent campaign of belief — running to prove they’re the best candidate in the entire primary, while also saying, ‘I’m electable and this is possible’ for a woman,” said Kelly Dittmar, a scholar at Rutgers University’s Center for American Women and Politics. “For women, there’s additional costs in time, in energy, in resources, in money to make this double case to donors, to political operatives, to the media and to voters.”

The challenge is apparent in public and private polling. The New York Times/Siena College poll of battleground states found that 41 percent of Biden supporters who didn’t support Warren in the general election agreed with the statement that most of the women who run for president “just aren’t that likable.”

Internal presidential polling and focus groups also showed the roots of gender bias, as voters grappled with electability. A source familiar with the Gillibrand campaign said they found “voters said they would have no issues with a woman, but they worried that other people might have issues.”

That feedback “shows deflection, and actually is more of what that individual thinks,” the source continued. “Most surprisingly, the comments came from women themselves, including younger women, not just older women, who have traditionally been most harsh on their own archetypes.” At the same time, surveys and interviews with dozens of voters show that many women at least say they are enthusiastic at the prospect of voting for a woman.

The candidates have seen the dynamic at play on the ground. Canvassers for a rival presidential campaign approached Klobuchar in a hotel lobby here on a recent evening to talk about sexism — and how voters are wary that a woman can’t beat Donald Trump.

“They just couldn’t stop talking about it. They felt sorry for me and [Elizabeth Warren],” Klobuchar said, dropping her voice down into a whisper. “They were like, ‘It’s so bad.’”