Bernie Sanders rallies, which have become renowned of late for their St. Francis dances with the animals vibe, lost a bit of their mystique on Wednesday in Philadelphia, when the Vermont senator said something that stuck in the craws of many: that Hillary Clinton isn’t qualified to be president.

She has been saying lately that she thinks I am not quote unquote qualified to be president,” Sanders said. “Let me just say in response to Secretary Clinton: I don’t believe that she is qualified if she is, through her super-PAC, taking tens of millions of dollars in special interests’ funds.

Sanders, who has since walked back his comments, was responding to Clinton’s critique of his interview with the editorial board of the New York Daily News, in which he stumbled over the details of his plan to break up the banks. “He’d been talking for more than a year about doing things that he obviously hadn’t really studied or understood, and that does raise a lot of questions,” Clinton said.

In his Philadelphia remarks, Sanders was attempting to make the basic argument of this election — that “outsiders” are more qualified than “insiders” to run the country at this particular moment. But calling Clinton, a former U.S. senator and secretary of state, “unqualified” is raising ire as a gendered attack, although that didn’t appear to be Sanders’s intention.

While 2016 campaign discussions of sexism have largely been preoccupied with Donald Trump’s blunt force assaults on modern notions of manners, let alone gender equity, Sanders’s remarks and their interpretation play into discussions of the subtle, pernicious forms of sexism that women in positions of power must deal with.

At the core of Clinton’s candidate packaging is the idea that she has for decades been the competent woman behind the scenes — a workhorse, not a show pony.

Clinton is not alone among her cohort in having highly burnished credentials; most female politicians are more qualified than their male counterparts, according to a 2013 paper by political scientists Kathryn Pearson and Eric McGhee. Looking at non-incumbent congressional races from 1984 to 2010, and which candidates had held elected office at a lower level — their metric for qualification — the researchers found that “women candidates in both parties are indeed more qualified than men.”

Why the extra layer of concern on the part of female candidates?

For one thing, there appears to be more self-doubt on the part of these high-powered women. A 2004 report by Jennifer Lawless and Richard Fox found that of a pool of prospective candidates — lawyers, business people, political activists — men were about twice as likely as women to say that they were qualified to run. Twenty-eight percent of women said they weren’t qualified at all, while only 12 percent of men found themselves lacking in some way. In the pop psychology parlance of 2016, we might note a whiff of imposter’s syndrome in these numbers.

It might not come as a surprise that just as women generally hold themselves to a higher standard in their self-examination before running for office, voters measure female candidates by different metrics than male candidates; there’s a very specific type of scrutiny that women politicians fall under. Women who might run for office seem to intuit that; a 2015 paper from the political scientists Kristin Kanthak and Jonathan Woon found that women are “election averse.” “Women’s entry into the candidate pool increases only if we simultaneously guarantee that campaigns are completely truthful and eliminate the private costs of running for office,” Kanthak and Woon found.

In a memo out this month from Lake Research Partners, Chesapeake Beach Consulting and the Barbara Lee Family Foundation, titled “Politics is Personal: Keys to Likeability and Electability for Women,” suggestions such as “Voters like informal photos of women candidates engaging with children” and “Voters like women officeholders who share credit with their teams, in addition to taking credit as an individual leader,” were on offer.

The memo, of the brass tacks strategy variety, says quite a bit about the line that female candidates must walk. “Women face a litmus test that men do not have to pass,” reads a passage in the document. “Women have to prove they are qualified. For men, their qualification is assumed.”

That’s why Sanders’s statement about Clinton’s qualifications cuts so deep — it seemed to send a volley at the fortress of qualification female candidates build up as proof of their worthiness to the public at large.

As a woman running for president, Clinton has been placed in a very particular gender bind; she is eager to showcase her impeccable resume yet quick to point out, in this year when voters have turned up their noses at establishment candidates, that being a woman in politics is an inherently outsider position. Sarah Palin and Wendy Davis have played on this same underdog — or “maverick,” as the case may be — note before.

Whatever the intent of Sanders’s original comments, language and all its hidden codes unspool during election years; its effects are pondered all the more. Karthak, co-author of the 2015 paper on women’s election aversion, took to Twitter this week to muse about the greater implications of Sanders’s comments.