And yet, Democrats emerged from Trump’s inaugural completely excluded from federal power, with Republicans simultaneously controlling the White House, House, and Senate. In state governments, Democrats began the Trump era at a low ebb, too.

So for many of those I spoke with, the march’s first purpose was to find reassurance that they were not isolated in their undiminished opposition to Trump. “More than anything we want to feel that we’re not alone,” said Mina Olivera from West Los Angeles, who marched with her husband and two children. “We just cannot be quiet and let it happen.”

Olivera’s simple declaration captured what is likely to be the march’s most important political impact. The unprecedented turnout—which by the best estimates drew about one in every 100 Americans into the streets—sent the message that even after Trump’s upset victory there is a still a huge mass of Americans viscerally opposed to him. “We’re trying to show we have a voice and we’re not scared,” Roger Palencia, a marcher from Whittier, California, told me.

For many marchers, that message’s principal audience wasn’t Trump, or even congressional Republicans. Instead, the target was congressional Democrats, who protesters expected to do whatever they could “to hold the line” against Trump, as Erica Mayorga of Whittier put it.

That sentiment is where a comparison to the Tea Party movement may be most aptly applied. The Tea Party eruption in summer 2009 had no discernible impact on then-President Obama’s decisions, and relatively little on congressional Democrats’ either. But the uprising sharpened congressional Republicans’ resistance to Obama. The effect was particularly evident on health-care reform, when the Tea Party’s emergence doomed Obama’s hopes of reaching a bipartisan Senate agreement.

It’s true, as skeptics have noted, that even if the women’s marches inspire sustained activism, that wouldn’t answer the key long-term challenges Democrats face. Based predominantly, though not exclusively, in urban areas, the marches reflected the excessive concentration of Democratic support in big cities and coastal states—a concentration that largely explains why the party holds so little power despite consistently amassing a bigger national coalition than the GOP since the 1990s.

But movements usually matter more in generating opposition than in formulating alternatives; they typically function more as a red light than green. It’s difficult, for instance, to see Trump’s rise as a policy victory for the Tea Party movement. Trump’s agenda on several fronts, like infrastructure and health-care spending, could even revive the “big-government conservatism” of George W. Bush that infuriated Tea Partiers. Still, by creating demand for a more militant party, the movement reconfigured the GOP and helped pave Trump’s bellicose run to its nomination.