Alex Ellison, a senior at Boston’s Emerson College, was thrilled by what she saw at the women’s marches over the weekend. She called her uncle, and Rep. Keith Ellison listened as the niece he had 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., said 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, and some 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 President Trump and congressional Republicans.

Many Democrats agreed with Sen. Chris Van Hollen, D-Md., chairman of the Democratic Senatorial Campaign Committee, who said Trump’s election had “woken a sleeping giant.”

In 2014 and 2016, he had 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 Connolly, D-Va., who attended the march with his wife and daughter, 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. …. I sensed a certain fervor and determination in that regard that was very heartening.”