Bernie Sanders’ campaign has been marked by the huge crowds turning out to his rallies, packing arenas with 20,000 people or more. But the key to his staying power in the 2016 race lies in more modest venues — living rooms, libraries and Internet chat apps — where his campaign turns the senator's online fans into a volunteer army that surpasses anything seen in presidential politics.

Barack Obama's successful campaigns in 2008 and 2012, for all their digital accomplishments, never fully achieved their ambition of converting online support into a volunteer force that could do the grunt work of cold-calling voters or knocking on doors.


But Sanders’ team has — honing a strategy of turning "slacktivists" who don't normally engage in grass-roots politics into an advance team capable of doing everything from managing phone banks to planning high-level campaign events. As of early April, his tens of thousands of networked volunteers had made 47 million phone calls, putting them on track to surpass the calls made by Obama’s operation during the entire 2012 election cycle.

Sanders’ organizational success — fueled by free or low-cost, off-the-shelf apps like Hustle and Slack — is the lesser-known counterpart to his campaign’s prowess in raking in campaign cash from hordes of shallow-pocketed donors online. Experts in the evolution of technology in political campaigns say these innovations have helped Sanders put up a far more vigorous than expected challenge to Democratic front-runner Hillary Clinton, including his 13-point win in Tuesday’s Wisconsin primary and his 12-point victory Saturday in Wyoming.

"Sanders' team is investing a lot of time and energy into thinking how to do things differently, how to build a distributed operation that translates into dollars and volunteers," said Daniel Kreiss, a former political organizer who wrote the book “Taking Our Country Back: The Crafting of Networked Politics from Howard Dean to Barack Obama.”

While Obama's campaigns broke new ground in bridging the offline and online divide, "here the scale is different, the technology has changed, and every step along the way that creates greater scale, greater speed and lowers the cost of mobilizing a digital base in the service of electoral politics," said Kreiss, a media professor at the University of North Carolina in Chapel Hill.

On the money front, the signs of Sanders’ success are undeniable. In March, the campaign announced it had raised $44 million, about $15 million more than Clinton did that same month. Nearly all of Sanders' donations, about 97 percent, came in online, part of a push led by the D.C. firm Revolution Messaging.

Less well-known is Sanders' digital field organizing, a tactic that stretches those campaign dollars. Sanders' virtual volunteers do campaign work that has traditionally been handled by paid operatives or fallen through the cracks in a busy election cycle — such as identifying likely voters or turning out people to campaign events.

The goal is to till the ground in primary and caucus states so that when Sanders' paid staffers arrive, they can devote their attention to voters who aren't yet sold on the 74-year-old democratic socialist.

"We've been able to engage people in voter contact no matter where they are in the world," said Claire Sandberg, the digital organizing director for the Sanders campaign and a former anti-fracking activist. The volunteers are “running huge chunks of the campaign," said Zack Exley, a Sanders adviser and veteran of MoveOn.org and Howard Dean’s 2004 White House run.

Developing the model has been the product of trial and error. While email has raised millions of dollars, direct email solicitations largely failed to get supporters to donate their labor.

"We could email a million people who said they wanted to volunteer, and we would get just dozens actually making calls," said Exley.

They found, however, that email could fill seats at events known as "barnstorms," organizing rallies where Sanders' digital staffers update supporters on the campaign’s strategy in cities across the country like Stockton, Calif., and Kansas City, Mo. And those in-person gatherings provided fertile ground for recruitment.

People who turn up for the barnstorms are asked to circle dates on paper sheets when they are willing to host neighbors at their home or, say, the local library, for a phone bank for Sanders. Completed forms are photographed, then uploaded online using Google's free Form tool.

Volunteers from Sanders' data entry team then type the information into a website that populates an online map plotting out the campaign’s phone banking get-togethers, canvassing operations and pamphlet-distribution events across the country. An unpaid scheduler calls people who've offered to host events to confirm details and answer any questions.

Nationwide, Sanders' volunteers have included 50,000 people making phone calls. In Wisconsin alone, more than 3 million calls flooded the state on his behalf, the campaign said.

Some say the jury is still out on the effectiveness of the volunteer-heavy approach.

“Making it easier to manage volunteers remotely is really exciting and innovative, but I do wonder if they’re getting the highest possible return on their investment in volunteers without a staffer to help them out," said Jesse Thomas, a Clinton backer and onetime Obama campaign field and digital organizer.

"Where I see [Sanders] failing to meet his targets” — the margins of victory needed to make his nomination mathematically possible — “you wonder if that’s where he’s starting to see the shortcomings of the fully distributed model, as opposed to staff touches,” Thomas said.

The Sanders camp is certainly doing traditional organizing, too. According to a recent Federal Election Commission report, Sanders has 865 people on his campaign payroll, more than Clinton’s reported 765 staffers.

A spokesman for the Clinton campaign pointed out that her digital operation has functioned well enough that she has garnered some 2.5 million more votes than Sanders has won thus far. But the Sanders' team argues that its distributed organizing strategy will fully reveal its strength as the election reaches sprawling states later in the calendar, such as New York on April 19 and California on June 7.

The virtual water cooler for Sanders volunteers is the group chat app Slack, popular among Silicon Valley start-ups and big media companies, which allows thousands of volunteers to share best practices and organize shifts. (The Sanders campaign is still using the free version of the software, which means it can keep only the last 10,000 Slack messages.)

The campaign has also turned to the texting app Hustle, which lets the volunteer Text for Bernie team — about 1,200 people — send personalized texts at the rate of a bulk email marketer to get people to phone banks. (The messages look like they come from local area codes, to avoid the stigma of the campaign parachuting in to a state.)

Then, during an actual phone bank, unpaid live-chat support agents are there to hold hands with volunteers as they cold-call strangers using Web-based software called LiveVox. While auto-dialing software would speed up the process, federal rules restrict the technology's use with mobile phones. So a team of about six hundred volunteers manually rings one number after another.

“We have an actual human sitting there" — wherever there is — "and placing the call," says Sandberg.

"The longer this goes on," she adds of the primary race against Clinton, "the more time we have to organize."