The Women’s March on Washington drew massive protests in the District and beyond. (Amanda Voisard for The Washington Post)

Alex Ellison, a senior at Boston’s Emerson College, was thrilled by what she saw at the women’s marches. She called her uncle, and Rep. Keith Ellison listened as the niece he’d struggled to get involved in the 2016 campaign described how inspiring it was to be surrounded by women, fighting for a cause.

“I was like — oh, now you’re interested?” Ellison (D-Minn.) remembered with a laugh.

The scale of Saturday’s marches, in Washington and elsewhere, surprised even the most optimistic boosters. Democrats who had tried and failed to generate enthusiasm for Hillary Clinton saw crowds conquering cities, as well as small towns she’d badly lost.

But after a day of massive protest, the party, and liberals more generally, are left to wonder what comes next.

Just as Republicans once adapted to the emergence of the tea party movement, Democrats are trying to figure out what a new — and much larger — mobilization will mean for the fights against Trump and congressional Republicans. Saturday’s marches, which featured speeches from many leading Democrats, were not explicitly Democratic events. Ellison, like all but one leading candidate to run the Democratic National Committee, spent the hours around the march at a donor meeting in Florida.

U.S. Rep. Keith Ellison (D-Minn.) is among the candidates to be the next chair of the Democratic National Committee. (David Zalubowski/AP)

At that meeting, talk of the march and viral photos of the crowd sizes and witty signs brightened up what had been conceived as a Democrats-in-the-wilderness summit. “People recognize the dangers Trump represents and they’re energized to take back our country,” said David Brock, who organized the Democracy Matters event in Florida. “We must channel yesterday’s energy into action and I have no doubt we’ll be successful. What the world saw yesterday was only the beginning of our resistance.”

That resistance belongs to no one group. Women’s March organizers created an intersectional event, its manifesto imagining a world where women “are free and able to care for and nurture their families, however they are formed, in safe and healthy environments free from structural impediments,” but saying nothing about electoral politics.

Many Democrats agreed with Sen. Chris Van Hollen (D-Md.), chairman of the Democratic Senatorial Campaign Committee, who said that Trump’s election had “woken a sleeping giant.” In 2014 and 2016, he’d watched Democrats in Maryland, then the Rust Belt, lose seemingly gift-wrapped elections as their base stayed home and the Republicans made gains. On Saturday, after he spoke to marchers, he joined them in a crowd that was too big to march through the city. The enthusiasm gap seemed to be vanishing before his eyes.

“There were a lot of people saying, ‘We wish we had this in November,’ ” Van Hollen said. “We need to harness that energy in the weeks and months ahead. The Senate’s going to be the main battleground; we need people to sustain what we saw on Saturday and fight the battles.”

Rep. Gerald E. Connolly (D-Va.), who attended the march with his wife and daughter and opened his Capitol Hill office for the day, said his last experience with a protest that big was the counter-inaugural to President Richard Nixon’s election.

“The next stop is organization,” he said. “We need to correct the cracks in the political structure that didn’t work as well as it should have in the last election and that means organization in every town and every small place and big space in the country. I sensed a certain fervor and determination in that regard that was very heartening.”

Connolly urged the anti-Trump masses to set their sights on the 2018 midterms as a chance to put a real check on the administration and test “the ability of those who have a different point of view to organize and deliver.”

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If the past is any guide, he said, the contrast could be striking. In 2009, in the only gubernatorial races in the country, Virginia and New Jersey installed Republicans Robert F. McDonnell and Chris Christie. The year before, both states favored Barack Obama for president.

Rep. Jamie B. Raskin (D-Md.), who hosted 1,500 at a pre-march breakfast in Silver Spring, Md., said the outpouring of support for progressive politics at the march could change the political dynamics in Congress.

“The political environment is going to be much more hospitable to Republicans who break ranks with Trump rather than those who toe the party line,” he said. “We know that the GOP places emphasis on party discipline. It will put a number of them in a tough spot.”

Raskin said that if he were head of the Democratic National Committee — a job he does not want, he noted — he would launch a program to put the young people who attended their first big march Saturday to work.

“In terms of the Democratic Party, I think that our strategic pathway is clear,” he said. “We have got to go on a consultant and pollster fast for a while. And we should put that money into organizing.”

Rep. Don Beyer (D-Va.), who like Connolly and Raskin represents a heavily Democratic district, urged people to direct their discontent into “good and noble” causes, like Big Brothers Big Sisters and Meals on Wheels, and run for precinct-level offices.

“If we can channel all of that action into political action and specifically precinct action,” he said, Democrats could take back the GOP-controlled Virginia House as well as the U.S. House and win the governor’s race. Though Beyer said he wasn’t predicting any outcomes, he said the steep drop-off in voter participation in a nonpresidential year presents the party with a clear challenge — one that amounts to a 98,000-vote difference in his Northern Virginia district alone.

“I deeply believe the world works by invitation,” he said. “Something to be exploited from these rallies around the country is to turn them into political activists.”

Neera Tanden, the president of the Center for American Progress, who marched in Washington, predicted that “many of those women are calling congressional offices and will go to town halls. And all of them will vote in 2018. The energy is growing, not diluting. Every day, Trump builds the opposition.”

Melissa Byrne, a candidate for DNC vice chairman, said that the larger-than-expected crowds showing up for protests will encourage even more people to become activists. But having organized for Obama’s 2008 campaign and for the Occupy D.C. movement, she saw how the new activists would be tested even if the rallies grew in size.

“People are going to get frustrated, because you want your wins to come quickly,” she said. “For people who are new to this, it takes a while to get that.”

But the size of the rallies, and the speed with which they were put together, seemed like an early win to their participants. In the campaign, Trump had promised to blow up not just the Obama legacy but a long liberal consensus on issues such as immigration and consumer protection.

“It doesn’t feel early to me,” said Leigha LaFleur, 42, an Oregon delegate for Sen. Bernie Sanders (Vt.) who came to the march in Washington and knitted 13 pink pussyhats for friends. “I think people were wanting this on November 10. And even though he’s been president since Friday, he’s already been doing things that affect people’s lives.”