Hillary Clinton entered the 2016 Democratic presidential race with the biggest campaign fund-raising operation in American history. But her upstart primary opponent, Bernie Sanders, outraised her. How? Sanders relied on ActBlue, a Somerville nonprofit that has become one of the most important and innovative political fund-raising organizations in the country.

Housed in an unassuming warehouse next to the Rosebud American Kitchen & Bar in Davis Square, ActBlue was founded in 2004 by two scientists (one an unsuccessful candidate for Cambridge City Council) as a platform for collecting low-dollar donations. Since then, ActBlue has amassed $1.6 billion in small contributions for Democratic candidates. It makes its platform free to left-leaning candidates and groups, charges nearly 4 percent for processing, and pays for its 50-person staff using donations.


It also has revolutionized American politics. Candidates can succeed not only by courting a handful of rich people over chicken dinners but also by attracting a wide spectrum of donors who give small amounts online. “Our mission remains the same since day one: to democratize the least democratic part of campaigns: fund-raising,” says Erin Hill, ActBlue’s executive director since 2009.

The Trump phenomenon also has been good for ActBlue. In the first three months of 2017, the organization’s platform collected 4.1 million contributions worth $111 million. That’s up from $17 million in 2013.

James Pindell is a Globe staff writer. Send comments to magazine@globe.com. Follow us on Twitter @BostonGlobeMag.