Nadia Milleron, an independent candidate for Congress, slipped off her shoes and climbed onto the bench of a picnic table. It was a muggy August evening, and gnats and mosquitoes were swarming the 50 or so people who had gathered for a campaign event in the garden behind a pizzeria in western Massachusetts.

Ms. Milleron was nervous. A neophyte candidate, she was trying to unseat one of the most powerful Democrats in Congress. That afternoon, she had twice rehearsed her short stump speech. In the barn next to her farmhouse, she had spent 10 minutes paddling a Ping-Pong ball against a makeshift backboard, a routine she had developed to ease her jitters.

She knew she faced long odds. But she also knew she had a potent weapon: her story.

Ms. Milleron had spent the last five years on a grief-powered crusade against an iconic but troubled American company, against regulatory inertia, against a legal system that she felt was intent on thwarting her. She had been inspired and at times directed by her uncle, the consumer advocate Ralph Nader.

If there was one core belief that animated the extended Nader family, it was this: Never underestimate the ability of tireless citizen activists to change the world. Ms. Milleron’s underdog journey seemed to validate that conviction. And her run for Congress was to her about more than politics. She was fulfilling a family obligation — and channeling anger and sadness that might otherwise overwhelm her.

“We thought as a family that someone ought to challenge Richard Neal,” her local congressman, Ms. Milleron told the small crowd outside Roberto’s Pizza in Sheffield, Mass. “I’m a lawyer, I’ve passed legislation, I’ve been effective.” She urged her supporters to donate to her campaign.