On Donald Trump’s first day in office, organizers of the Women’s March on Washington are calling on “all defenders of human rights” to join to stand up for women and other groups that have been marginalized.

But there is one group, composed of about half of the population, that is hard to find in the social media and logistical frenzy leading up to the highest profile event protesting Trump’s politics: men.

Of the 175,000 people who indicated they are going on the march’s Facebook page, just a fraction appear to be men. And the #WhyIMarch Twitter feeds show far more mothers and sisters than fathers and brothers. On the ground, march organizers in Houston, Cleveland and Pittsburgh reported that just a handful of the seats on their buses have been reserved by men.

“This is a movement that is led by women, but it is not just for women. It’s for all people,” said Linda Sarsour, one of the march’s lead organizers.

One caveat: “You have to be okay with being led by women,” she said.

(Elyse Samuels/The Washington Post)

The same test that played out when Americans went to vote for the nation’s first female president is now playing out in the anti-Trump response to the election. Some scholars of gender and politics say that while plenty of these men believe in women’s rights and abilities to lead, many still aren’t comfortable shouting their views through a bullhorn or spreading them on Twitter. Even those who show up might be unlikely to signal so beforehand.

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“A lot of men are quiet supporters of women,” said Jackson Katz, author of “Man Enough? Donald Trump, Hillary Clinton, and the Politics of Presidential Masculinity.” Millions of men voted for Clinton and support women’s rights both politically and personally, he said, but they don’t have a powerful voice.

Plans to attend the march formed quickly among female friends and relatives, many of whom also took to social media to channel their disappointment after the election.

Katz attributes the more muffled support among men in part to efforts that Trump and other Republicans have made to challenge the masculinity of men who support liberal causes or women in leadership. Trump has repeatedly cast himself as the strong man.

Alex Mohajer, co-founder of Bros 4 Hillary, an advocacy group, said it this way: “There is a sense [that] if you outwardly support a woman you are less deserving of your man stripes.”

The November election exposed the largest gender gap in more than 40 years, with women favoring Clinton by 13 points and men favoring Trump by 11 points. The gap was most stark for white men, in particular non-college-educated white men, 71 percent of whom voted for Trump. For this group of economically challenged men, Trump’s appeal to a simpler time when men ruled the family resonated, Katz said.

At the same time, millions of men went to vote for Clinton as the first female president. Among them, 82 percent of African American men and 63 percent of Latino men. Younger men — ages 18 to 29 — were also more supportive of Clinton and also are likely to support gender equality when it comes to a range of family-friendly policies.

Katz said these men will need to speak out if they don’t want to see abortion outlawed, given Trump’s pledge to appoint antiabortion judges to federal courts. They will also need to make known, he said, that they believe preventing sexual violence should be a priority, after Trump openly bragged about assaulting women.

“That means taking some risks in challenging other men, and literally standing up to the bullying that comes from the right about masculinity,” Katz said.

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Women are leading the charge for the march, heading up logistics and legal work, while male volunteers are playing mostly supporting roles. It is a contrast to the 1963 March on Washington, when women largely worked behind the scenes.

“This is all a part of straightening that bend in the road that women did not have a voice through the years,” said Harry Belafonte, the music legend and civil rights leader who worked with Martin Luther King Jr. and was asked to be an honorary co-chair of the event with feminist icon Gloria Steinem.

“A lot of women are going with their friends, their sisters, and their mothers,” said Leah Burnett, a musician who helped organize five busloads of marchers from Cleveland. “I think it’s a bonding experience.”

She counted less than 10 of more than 250 seats that she can confirm have been reserved by men.

Many men who have pledged support for the march on Facebook say they are motivated to attend to continue the progress that women have made.

Tim Riddick, a 36-year-old photographer from Woodbridge, said he plans to join the march because he wants to set an example for his three young sons.

“I am worrying about the way my boys will treat women when they are older. I want to make sure they not only respect women, but that they fight for women as well,” he said.

Riddick calls himself a “purple elephant,” a rare liberal who is also an observant Christian. He believes that women should be leaders in the church and also in the nation — and he believes women’s rights will not be successful without support from both genders. That means blending the line on what is considered a “women’s issue” to start with, including access to abortion and birth control.

Jeffrey Allan Ellis-Lee, a public school teacher in New York City, volunteered to be a bus captain, helping to shepherd a fleet of more than 60 buses that are scheduled to bring protesters from New York City and building on organizing work he did during Clinton’s campaign.

“This was such an anti-woman campaign,” he said. “There are so many issues, but this is the issue that I am standing up for during the march itself.”

Gerald Dudley, 33, is attending a solidarity march in Austin, where he works for a company that hosts pub quizzes. He said he wants to be much more outspoken in his support for women’s rights. “It’s not enough to say, ‘I’m not a misogynist,’ ” he said. “This year I am trying to put my money where my mouth is.”

To him, that means donating to feminist causes, seeking out more women’s perspectives in his reading, and calling out sexism when he encounters it. “When I hear a joke where the butt of the joke is a woman . . . Maybe I could say, ‘I don’t get it: Why is that funny?’ ”

Darren Battle, a 51-year-old chef in Atlanta, is coming to Washington for the march because he wants to support equal pay and other rights.

“There are not many female chefs. But if they are doing the job, they should be making what I am making,” he said.

Duncan Chaplin, an education policy researcher in Petworth, said when he heard about the Women’s March he immediately planned to go and invited friends from out of town.

“Being part of a loyal opposition is important,” he said. “I want to oppose what Trump stands for, and women’s issues are clearly a part of that.”

Emily Guskin contributed to this report.