It started out as a small grassroots movement, but when January 21 arrived the Women’s March on Washington turned into a protest of millions of people in 600 cities on all seven continents—yes, even Antarctica.

Under the leadership of gun-control advocate Tamika Mallory, the Arab American Association of New York Executive Director Linda Sarsour, The Gathering for Justice Executive Director Carmen Perez, and fashion entrepreneur Bob Bland, the march gained support from politicians and celebrities pushing for a range of issues, including women’s rights, immigration, and healthcare reform.

And as associations likewise leverage member support to host fly-ins and push legislative agendas, they too face the challenge of converting that momentum into a sustainable advocacy strategy.

“It’s really easy to go to rallies, and have fun there. … It’s very different to persuade your member of Congress to change their mind on an issue,” said grassroots and political action committee consultant and principal at The Showalter Group, Inc., Amy Showalter. “And that’s really what you’re charged to do as a grassroots effort; you’re there to change behavior, put that pressure on.” To maintain momentum, she encourages associations to take three steps following an initial event:

You can’t assume that they’re all going to march every week or every month or every year.

1. Offer tangible next steps. Following a rally or other event, organization leadership needs to provide clear next steps participants can take to get involved, beyond joining a mailing list or connecting on social media. A person’s decision to attend an event is largely based on time of year, the issue, and who’s going—and isn’t a sign of a committed volunteer. So to find committed individuals, encourage people to learn who their local elected officials are, connect and build relationships with those officials, and participate in an advocacy training session.

“You have to give them options on future engagement,” Showalter said. “You can’t assume that they’re all going to march every week or every month or every year.”

For example, the Women’s March on Washington’s 10 Actions for the First 100 Days campaign will continue engaging the protest crowds by sharing a new, practical way to push for change every 10 days. The first action: send a letter to your senator.

2. Develop local leaders. Successful advocacy efforts require enthusiastic volunteers as well as an infrastructure of local, authentic leaders able to engage volunteers and officials.

In addition to collecting contact information at local events, Showalter recommends sending talent scouts to identify volunteers who are inclined to lead, can build up other leaders, and have the right personality. To then support those individuals, organizations should offer leadership-development training and remind them of the group’s success stories to fight leader fatigue or discouragement.

“The organizational leaders have to create organizational icons and avatars that others follow and look at them and say, ‘Wow, they did this; I can do that too,’” Showalter said.

3. Manage expectations. Groups often lose their grassroots momentum when they set unrealistic expectations and aren’t clear that advocacy is a long-term process. Volunteers need to understand that changes don’t happen overnight.

“Those events many times are a catalyst for moving issues forward, for creating awareness,” Showalter said. “They’re one of the links in the chain for this ultimate result, but you’re not going to change the world with one tweet, or with one Facebook post, or whatever. It’s just not going to happen.”

A scene from Saturday's Women's March on Washington. (Shannon Stapleton/Reuters)