Updated on April 17, 2017 at 9:59 a.m.

On Saturday, protesters gathered in cities across the United States, and around the world, to demand that President Trump release his tax returns, in an early test of the strength and staying power of the grassroots movement that has mobilized in opposition to the new administration.

The tax marches may be the biggest political demonstration to take place since the Women’s March in January. But they were never expected to match the record turnout of that event, which has been estimated to be the largest mass mobilization ever recorded in a single day in United States history.

High turnout for the Women’s March focused attention on the record low approval ratings with which Donald Trump entered office, but it inevitably set a high bar against which future demonstrations will be compared.

“The Tax March is likely to be smaller than the Women’s March, but I wouldn’t necessarily say that’s a sign that activism has diminished,” said Erica Chenoweth, a professor at the University of Denver who tracks political protest crowd estimates. “For now, the Women’s March is definitely an outlier. It was a very unique day in U.S. history, but I wouldn’t say that means activists have maxed out their potential for mobilization. It just means we haven’t seen it matched yet.”

The Crowd Counting Consortium, a project that compiles crowd estimates for political events in the United States, has not yet finalized its own tallies for the Tax March, but event organizers claim that over 25,000 people showed up in Washington, D.C. on Saturday.

If that estimate holds, it would exceed the estimated turnout of 15,000 people in Atlanta in 2009, the largest recorded crowd size for a single Tea Party Tax Day rally. But the Washington Tax March crowd estimate is far smaller than the number of people who attended the Women’s March in D.C., which drew an estimated 725,000 people, according to the Crowd Counting Consortium.

Record-setting crowds at the Women’s March, as well as ongoing protests aimed at sending a message to the president like the Tax March, are clear indicators that Trump’s administation continues to drive grassroots activism. The Tax March is also just one of several protests scheduled to take place this month, including rallies in support of science and climate action.

The difference in crowd size between the Women’s March and the Tax March may be a function of the extent to which progressives perceive an immediate threat, and the scope of the event. The Women’s March was a chance to make a generalized statement of defiance to the incoming president. Trump’s tax returns are a more targeted focus.

“The reason the Women’s March was so big was that it was the first opportunity to stand up in resistance to the new administration. It was an explosive moment, like a cork popping out of a bottle,” said Joe Dinkin, a spokesperson for the Working Families Party, one of the groups helping to organize Tax March rallies.

“Today, we're looking at a sprawling movement of resistance to Trump that spans from weekly marches to thousands of town hall meetings, to elections,” Dinkin added. “The Tax March will be only a fraction as big as the Women's March, because the movement is expanding in so many different directions right now, but it will be big and it will prove how wrong Trump is when he says only the media cares about his taxes.”

Trump has indeed said that “the reporters” are “the only ones” who care about his tax returns, but polling indicates that in fact most Americans do want him to release them. The issue is one that both Democrats and Republicans care about, though Democrats seem to care more. In January, Pew Research Center found that 79 percent of Democrats said the president has a responsibility to publicly release his tax returns, compared to 38 percent of Republicans.

Even so, concern over the issue may have diminished over time. A Bloomberg/ Morning Consult poll conducted in April shows that 53 percent of voters believe the president should be required to disclose his tax returns, while 51 percent rank the issue as important. But as Time points out, that’s less than the 62 percent of voters who said that it was important for candidates to release their tax returns in a separate survey prior to the election.

Specific policy issues may galvanize liberals and progressives, in much the way that opposition to the stalled GOP attempt to repeal the Affordable Care Act did. But it may be challenging to maintain consistently elevated levels of activist participation when hot-button issues fade from the headlines. Protests may also arise in response to specific actions taken by the administration. When the administration banned travel from seven majority Muslim nations, thousands of people rushed to protest the directive in airports and cities across the country.

Even if future protests during the Trump era don’t match the size of the Women’s March, the demonstrations may have already set in motion a chain reaction that increases civic engagement and leads to significant political impacts.

Research published in 2013 in the Quarterly Journal of Economics found that the Tax Day marches convened by the Tea Party in 2009 were not just a symptom of political energy: They translated into increased Republican turnout in subsequent congressional elections, and inspired elected representatives who witnessed protests in their districts to vote more conservatively.

Ongoing demonstrations could be a harbinger of higher Democratic voter turnout in upcoming elections, and may help lay the groundwork for future movement building on the political left. In the aftermath of the election, progressive organizers have also been putting pressure on their members of Congress to oppose elements of Trump’s agenda by calling their offices and showing up at town halls across the country.

There are already indications that energized liberals are channeling their energy into elections. The Democratic candidate in a congressional special election in Kansas lost last week, but performed significantly better than political observers had predicted. Meanwhile, money has poured in at a rapid clip to bolster the Democratic candidate in an upcoming Georgia special election for a House seat.

Turnout for protests is just one part of a larger political landscape. Protests also can’t provide a comprehensive picture of how Americans feel about Trump’s presidency on their own. According to Gallup’s latest polling, 55 percent of Americans disapprove of the president. If Trump’s popularity sinks lower, there will likely be an uptick in opposition to his agenda, whether in the form of grassroots protest or pushback in Congress. If the president’s approval rating rises, there may be fewer protests, and smaller crowd sizes.