Sen. Bernie Sanders’ (I-VT) has led the crowded 2020 Democratic primary field in fundraising, cultivating a massive list of over one million volunteers along the way. Now, with the field largely set, following the entrance of former Vice President Joe Biden this week, Sanders’ team is putting that people-powered muscle to work.

On Saturday, the campaign launched a nationwide organizing program with nearly 5,000 house parties in every state throughout the country, demonstrating a show of force for his volunteer network and an opportunity to mobilize supporters in a primary contest that could remain close through the early voting states and beyond.

“If we’re going to defeat Donald Trump, we’re going to need a massive grassroots effort and that’s what today is about,” Sanders told The Daily Beast in an interview on Saturday. “Our job is to significantly increase our citizen participation and we think the agenda that we are fighting for, an agenda that works for all of us and not just the one percent is an agenda that can bring millions of people together to transform our economic and political life.”

In addition to the house parties, which Sanders spent part of the day calling into, the campaign also launched a new app called BERN which will be crucial to their strategy going forward. It allows for volunteers themselves to log conversations with voters, friends and family for the purpose of ensuring voter registration and getting Sanders’ supporters to participate in primaries and caucuses within their states.

This distributed organizing strategy, used in Sanders’ last presidential campaign as well as former Rep. Beto O’Rourke’s (D-TX) 2018 Senate bid, is different than a typical system in which volunteers are often only allowed to do this work with supervision from field organizers in various campaign offices. It eliminates the necessity for a campaign to need field offices and staff to oversee volunteers and allows for the campaign to get an early jump on outreach long before primary voting begins.

As Claire Sandberg, national organizing director for Sanders’ campaign explained, a volunteer can look up a voter, whether it’s someone they know personally or someone they meet in their community, and mark down whether that person is a Sanders supporter, undecided or backing another candidate.

“We have two main modes for the app: friend to friend mode and community canvass mode,” Sandberg said, noting that the first mode is more effective than talking to strangers. “They're both very similar, but in friend to friend mode volunteers can tell us if they know the voter. This is important, because in the future we'll want to ask volunteers to have conversations with their undecided friends, make sure that their friends who need to register or request a Democratic ballot get registered and know how to vote, and eventually make sure their friends turn out to vote or caucus for Bernie.”

In the previous campaign, Sandberg said that volunteers in New York were desperately trying to get ahold of a voter list to engage independents and even third-party voters to get them to switch their registration to vote in the Democratic primary, which needs to be done six months in advance in the state. The new app helps fix that problem and simply put “volunteers everywhere can have conversations with voters now, rather than having to wait for the campaign to arrive in their state or community.”

It’s a crucial next phase for the campaign, though one that Sanders has acknowledged bears a few risks, and a tactic that he thinks will differentiate himself from a sprawling field with other heavyweights. The Independent from Vermont is hoping that this engagement even helps level the playing field when it comes to social media, where he noted that President Trump dominates the Democratic contenders with nearly 60 million followers on Twitter alone. It also comes after Biden outraised the first-day totals of other candidates in the field, though with fewer individual donors than Sanders and a high-dollar fundraiser as well.

“It’s a grassroots campaign funded by grassroots low donor contributions and that’s why I think we win,” Sanders told The Daily Beast. “That’s why I think we are going to win. I’m excited about what’s happening today and I think it’s a very good omen for the rest of the campaign.”