CHICAGO — Sen. Bernie Sanders flaunted his ground operation Saturday with what he called the “largest distributed day of action ever in a presidential campaign” and announced a new online organizing tool called BERN.

“We need to put together the strongest grassroots movement in the history of politics,” Sanders said in a pre-recorded video played for more than 4,700 volunteer-driven organizing kickoff events nationwide. “And we’re off to a good start!”

The online tool allows everyday supporters to contribute to the campaign’s voter database by logging names and background information of anyone from a family member to a stranger met at a bus stop. It matches each name to a voter record before noting their level of support, priority issue and even union membership.

Sanders began the race with a strong field operation, largely thanks to his 2016 run and a supporter list that only grew in the subsequent years. The organizing kickoff highlighted what the Sanders campaign considers a significant priority and a major advantage in the crowded Democratic primary field.

“Many voices will attempt to diminish what we’re building here together and argue that our movement has run its course,” national organizing director Claire Sandberg told organizers in the campaign video. “But the reality is,” Sandberg continued, “we grow larger every day.”

Sanders says he has more than 1 million people signed up to be part of his campaign. In the first quarter of 2019, his campaign outpaced the field, earning 900,000 donations from 525,000 individual donors.

At each campaign rally, volunteers digitally and meticulously collect the email address and phone number of every attendee. The Sanders campaign said around 30 percent of rally attendees are new to the campaign data lists.

Supporters Saturday were trained on how use the online tool and were encouraged to immediately begin mobilizing and growing the organization.

“Traditionally, it seems like to get this information to the campaign you need to either call voters or knock on their doors,” said Chris Wilson, a University of Chicago student who joined after a campus event.

Wilson’s first foray into politics was making calls for a young, little-known bartender named Alexandra Ocasio-Cortez, who was running a primary campaign in his home state of New York.

“Now we have all these people across the country distributed everywhere, and they can start putting people into the system,” Wilson said.

He said he “dragged” his friend Shannon Sheu, who is undecided, out on a snowy April afternoon to the organizing event.

“It significantly lowers the barrier to entry to actually help and make a difference,” Sheu said, impressed by its compatibility with people uncomfortable with political conversations. “You plug in people’s names and you let other people send the emails.”