Much of Hillary Clinton’s difficulty in this campaign stems from a single, unalterable fact: She is a woman.

I’m not referring primarily to the Bernie Bros, those Bernie Sanders supporters who fill the Internet with misogynistic filth about Clinton. What drags down her candidacy is more pervasive and far subtler — unconscious, even.

The criticism is the same as in 2008: She doesn’t connect. She isn’t likeable. She doesn’t inspire. She seems shrill. “She shouts,” Bob Woodward said on MSNBC this month, also suggesting she “get off this screaming stuff.”

Joe Scarborough, the host, agreed: “Has nobody told her that the microphone works?”

At that, Clinton supporters hollered — about the double standard that condemns her but not Sanders, who bellows at the top of his lungs. The episode was part of a constant stream of commentators (generally men) taking issue with Clinton’s demeanor and conduct — “She’s got to become herself,” David Gergen advised on CNN before Thursday night’s debate — in a way they don’t do with Sanders.

At a Clinton rally last week in New Hampshire, I discussed the decibel dilemma with Jay Newton-Small of Time magazine. “It’s very hard for a woman to telegraph passion,” she explained. “When Bernie yells, it shows his dedication to the cause. When she yells, it’s interpreted in a very different way: She’s yelling at you.”

That’s not about Clinton; it’s about us. “It is a subtle kind of sexism that exists that we don’t recognize,” said Newton-Small, who literally wrote the book on the matter. “Broad Influence: How Women Are Changing the Way America Works,” out last month, includes a chapter on Clinton. “When women raise their voices, people tend to get their hackles up. People I talk to at Clinton events put her in a maternal role: Why is she screaming at me? Am I in trouble?”

Campaigning While Female also deprives Clinton of the ability to make lofty promises. Sanders, for example, has a $15 trillion non-starter of a health-care plan. If Clinton floated such a plan, the media would mock it as patently absurd. But Sanders gets a pass.

Why the double standard? “Men are the guys who want to go out and buy the motorcycle, and women are the purse-string holders,” Newton-Small said. “It’s a very traditional role we are putting women into by making them the one saying, no, we can’t do all these really fun things. This is a very stereotypical box she gets put into, which then makes it very hard for her to be inspirational.”

This is the essence of Clinton’s trouble: If she can’t plausibly offer pie in the sky, and she can’t raise her voice, how does she inspire people? This hurts particularly with young voters — the same segment that shunned Clinton in 2008.

Clinton’s “likeability” problem also has something to do with her lack of a Y chromosome. It’s a direct consequence of the imperative that she demonstrate her toughness. Men can be tough and warm at the same time — think Ronald Reagan — but for women, it’s a trade-off.

In 2008, she played down gender and positioned herself as “ready to lead on day one.” This time she took a softer approach but eventually found herself back in the position of arguing that she’d be a better wartime leader than Sanders. For Clinton, “it’s a really tough needle to thread to be tough enough to be a commander in chief and still be likeable,” Newton-Small said.

I disagree with those who scream “sexism” every time somebody criticizes Clinton. But there’s no denying that women are more often the victims of online savagery. That was true long before the Bernie Bros (who could be heard booing a mention of Madeleine Albright at Thursday’s debate). Sanders objects to the Bernie Bros but may encourage them when he talks about the “drama” Clinton creates and her “shouting.” It’s also hard to imagine a male candidate being faulted for his wife’s misbehavior the way Clinton is blamed for her husband’s.

There’s not much Clinton can do about this. But she can make the case that while Sanders talks “revolution,” her presidency actually would be one, because the first female president would govern differently from her 44 predecessors.

Clinton has been at the vanguard of the women’s movement for decades, but the movement has been so successful that young voters, even women, don’t realize how much has changed — and how having a woman as president could complete that Quiet Revolution.

“Women in general are better listeners, are more collegial, more open to new ideas and how to make things work in a way that looks for win-win outcomes,” Clinton told Newton-Small in “Broad Influence.”

Now that’s something worth shouting about.