Why are people marching?

From the beginning, the purpose of this march has been to challenge Mr. Trump’s administration.

“We’re doing it his very first day in office because we are making a statement,” one organizer, Breanne Butler, said in an interview days after the election. Of the the marginalized groups she accused Mr. Trump of attacking during his campaign, she said, “We are here and we are watching. And, like, ‘Welcome to the White House.’”

As the women’s group has become more organized, four co-chairwomen have refined the mission to specifically elevate groups like immigrants and minorities. Groups focused on immigration rights, including Define American and United We Dream, are partners with the group. Abortion rights will also be on the agenda: Naral Pro-Choice America and Planned Parenthood are both encouraging people to attend.

More than 30 other groups have joined as partners, including the Muslim Women’s Alliance, the Trayvon Martin Foundation, Girls Who Code and Black Girls Rock.