In the heat of a presidential race, sometimes it’s the inexperienced questioners who inspire the most passion in the candidates.

Hillary Clinton responded to a question about the unfair emphasis on women’s body image Tuesday night by giving what the New York Times called her “most potent” comment of the evening. At a town hall meeting in Haverford, Pa., when a 15-year-old girl asked the Democratic presidential candidate what can be done to get girls to understand that “that they are so much more than just what they look like,” Clinton offered up a vehement appeal. She said women need to “be the best we can be” and “be proud of who we are.”

When the question was first asked, Clinton leaned forward in her seat, smiled, and nodded repeatedly, telling the girl, Brennan Leach, that she was “so proud” of her for asking the question. The Democratic candidate went on to put the issue into the context of the campaign, saying that Donald Trump takes the issue of women’s appearance to a “new level of difficulty and meanness.” Clinton was, of course, referring to Trump’s string of derogatory remarks about the looks and behavior of women, including his chiding of former Miss Universe Alicia Machado, who he said gained too much weight.

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By and large, the media has used Trump’s commentary about women’s bodies in the context of his own campaign, assessing what such remarks say about his judgment and professional demeanor. But the Clinton campaign has been careful to raise the question of what his sexist comments mean for the self-esteem of women and girls today. Her team released an ad last month that plays audio of Trump’s remarks about the female physique over images of young girls examining their own physical features, with the kicker: “Is this the president we want for our daughters?” The message is a powerful one aimed at extending Clinton’s lead among female voters.

Young women’s body image has become a political talking point at a time when their satisfaction with their own physical appearance is on the decline. On Tuesday, the nonprofit Girlguiding U.K. released a study of more than 1,600 7- to 21-year-old females that showed that 61% of the respondents were “happy with how they looked.” The figure was down from 73% in 2011.

Susie McGuinness, an advocate at Girlguiding, chalks up the decline in how girls and young women feel about their bodies to the ubiquitous nature of Facebook, Twitter and Instagram. “This has to do with girls being on social media at a younger age,” McGuinness said. “It’s not as if girls see a photo of a model on a billboard—they can’t walk away from it because it’s on their phones.”

How a young woman feels about her appearance affects more than how she feels about herself. The same study also showed that concern about physical appearance prevents girls from participating in certain activities and social interactions. For example, 41% of girls aged 11-16 said low body confidence holds them back from participating in sports. At the same time, 39% of girls in that age group said it stopped them from speaking up in class. “It’s really upsetting because we know there are so many girls out there who are holding themselves back from reaching their full potential,” McGuinness said.

Clinton’s answer on Tuesday came before a friendly audience designed to play to her strengths, and some critics panned the question as being canned (Leach had some help from her father, who’s a state senator), but young girls need to hear body-positive messages, even if they’re scripted.

“The focus on body image is still at unacceptably high levels,” said Carole Easton, chief executive of the Young Women’s Trust, a nonprofit. “I’m absolutely with Hillary Clinton [in that] we need to be proud of who we are.”