On Saturday, November 3, three days before the midterms, 200 volunteers gathered in Modena, New York, to canvass for Antonio Delgado, an African American lawyer and first-time congressional candidate. A local field staffer, a cheery young man named Todd, told me that so many people had shown up around the district to help Delgado unseat incumbent Republican John Faso that the campaign was able to knock on 65,000 doors that day, nearly the same number of votes cast in the district during the last midterm election. The next day, Delgado’s supporters hit another 50,000—a small part of a massive surge in organizing that took place across the country.

On Tuesday, Delgado was elected in a Democratic wave that (nearly) achieved the scale the party had hoped for. The wave crested in formerly Republican-leaning House districts all over the country, lifting first-time candidates like Abigail Spanberger in Virginia, Mikie Sherrill in New Jersey, and Kendra Horn in Oklahoma, and ultimately delivering the House to Democrats for the first time since 2010. It wrested seven governorships from Republicans, and while the wave wasn’t big enough to lift Andrew Gillum in Florida or Beto O’Rourke in Texas, they demonstrated unexpected strength in their campaigns.

There will be many explanations for these victories, but the sheer size of the volunteerism was clearly a deciding factor. The mobilization was not merely unprecedented for a midterm; it reached levels typically seen only in a presidential year. More important, activists developed new and different approaches to mobilizing the volunteers who were phone banking and knocking on doors this fall. Traditionally, most electoral organizing has been run through campaign committees that command powerful lists of millions of activists, donors, and volunteers. (Barack Obama, for example, had 13 million names, 3.95 million donors, and 35,000 volunteer groups on his 2008 list.) That model was already breaking down in 2016, with outside groups like Color of Change, Feel the Bern, and 350.org operating independently of the Democratic establishment. Two years later, however, liberal organizing has now spread out to dozens of independent national groups and thousands of local ones, most of them completely new and not directly connected to the party.

It didn’t have to be this way. Barack Obama’s field operation in 2008 was the best in a generation, but at its root, it was still conventional, an army commanded by field generals who closely managed its actions. Although the arrangement gave the Obama campaign highly effective control, it meant that when he was elected, his former campaign manager, David Plouffe, could mothball the entire apparatus, folding Organizing for America, and its 13-million-member email list, into the Democratic National Committee as a fully controlled subsidiary—a choice that sapped grassroots energy from the Democratic Party and contributed to its losing 968 state legislative seats over the next eight years.

After the disaster of Trump’s election, there was no organizing structure in place to come rescue the party. Into that vacuum came a new cohort of activists. To begin with, older women and younger but more experienced Democratic campaign staffers launched Indivisible. From a Google Doc started by a group of young congressional aides, it spawned 6,000 local chapters (at least two in every congressional district). The Women’s March prompted the launch of thousands of local huddles. And soon, a long list of new groups emerged to direct campaign knowledge, data, and resources wherever they were most needed.