Ms. Nelson says she is convinced that, while a vanishing fraction of Americans belong to unions, workers are increasingly fed up with their lot and amenable to the idea of taking on their bosses directly. After she gave the speech calling for a general strike, a labor historian asked her whether it was too dangerous to talk about publicly. “Strike, strike, strike, strike, strike, strike, strike,” Ms. Nelson told him. “Say it — it feels good.”

Her vision reflects the restless energy upending the Democratic Party today and the populist fury that drew many blue-collar voters to Mr. Trump. It is also what has some union leaders hoping she’ll gun for labor’s top job as the leader of the nation’s largest federation of unions, the A.F.L.-C.I.O., the next time it opens up.

In Senator Sanders’s office, Ms. Nelson said she had been initially hesitant to attend that night’s address “and listen to a bunch of lies,” but had come around to the idea. “It would be really good to be standing there and feeling like I was on equal ground,” she told me. With whom, I asked. She didn’t hesitate. “With all the powers that be, up to and including the president of the United States.”

‘I could stab you right now’

Ms. Nelson grew up in Corvallis, Ore., a city with small-town vibes. Her parents, a music teacher and a lumber worker, were Christian Scientists — a religion established by a woman who espoused gender equity. The church, Ms. Nelson said, taught her that “male and female qualities can be expressed by anyone.”

Early dreams of working as an actress didn’t pan out, and Ms. Nelson graduated from a Missouri college with about $45,000 in student debt. She spent nearly a year holding down four jobs — waiting tables, selling linens, substitute-teaching and temping at an insurance company. When she found out United had openings for flight attendants in 1996, she drove 300 miles to Chicago to audition.

By then, United had generally stopped making applicants step on a scale to meet a weight requirement. The airline did measure Ms. Nelson’s height (an acceptable 5-foot-4), and when she got the job, they checked her hair (wispy and blonde) to make sure it did not rebel against an updo.

She spent six weeks in training, which included a “makeup day” when the men took the day off and the women learned how to apply mascara. This was helpful to Ms. Nelson, “a granola from Oregon,” she said, who had never worn any.