The foundation that paid for the trip, and for the “Fed Up” campaign that Mr. Barkan mounted in its aftermath, wrote in an internal assessment that it didn’t see much chance Mr. Barkan would succeed in influencing monetary policy. But that November, Ms. Yellen met with 30 workers led by Mr. Barkan in the Fed’s ornate boardroom in Washington. Two years later, in August 2016, the Fed’s summer retreat opened with a new event: Eight of the Fed’s top officials attending a meeting with “Fed Up” participants, listening to their stories.

Just a few weeks later, Mr. Barkan was spending a Sunday morning with a friend he had known since kindergarten, who happened to be a neurologist. He mentioned that his left hand felt weak, and she offered to take a look. By the end of the week, he had been told he was dying. He had just become a father; the doctors said he would be lucky to see his son turn 4.

For almost a year, Mr. Barkan allowed the imminence of death to dominate his life. But by the fall of 2017, he felt useless and restless. He wanted to spend time with those he loved, but he did not love the way he was spending time: He had lost a sense of purpose. He wanted to be a good father, but he was losing the ability to hold his son .

As congressional Republicans moved to pass a large tax cut, Mr. Barkan decided to cast himself in the role he had so often persuaded other people to play — as a living symbol of the stakes. He flew to Washington to protest the bill, arguing that tax cuts would be a prelude to spending cuts — including reduced spending on federal health insurance programs. Headed back to California, he found himself on the same flight as Senator Jeff Flake, Republican of Arizona, and he urged the senator to “ Be a Hero ” by opposing the cuts. A video of their conversation went viral .

Mr. Barkan capitalized adeptly on that celebrity. Seeking to punish Senator Susan Collins of Maine for supporting the legislation, he hit on the idea of funding her “future opponent” in 2020, whoever that may be. So far, he has raised almost $3.8 million. During the midterm elections in 2018, he went on a nationwide tour, speaking before thousands even as he was losing the ability to speak.