Bernie Sanders's presidential campaign says the Democratic candidate drew 28,000 people — its largest crowd yet — in Portland, Ore., on Aug. 9. (Sarah Parnass/The Washington Post)

Presidential hopeful Bernie Sanders, who has been drawing eye-poppingly large crowds on the campaign trail, on Sunday night attracted his largest audience yet: about 28,000 people in Portland, Ore., according to staff at the venue.

Sanders, the independent senator from Vermont who has emerged as the leading alternative to Hillary Rodham Clinton for the Democratic nomination, appeared at a Portland arena with a capacity of 19,000. An additional 9,000 people gathered in overflow areas set up for the event, said staff from the venue.

“Whoa! Unbelievable!” Sanders said as he took stage at the Moda Center, where the NBA’s Portland Trail Blazers play.

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Sanders decried the political influence of the “billionaire class” and promised a better lot for the working class, including a minimum wage increase, expanded Social Security benefits and free college tuition. His appearance in Portland was live-streamed on his campaign’s Web site.

Sanders, a self-described democratic socialist, has drawn larger crowds than any candidate from either party to this point in the 2016 cycle. His largest crowd to date was on Saturday night, when he drew about 15,000 people to an arena in Seattle.

By contrast, Clinton's largest crowd, which her campaign estimated at 5,500, came at her formal kickoff in June in New York.

Sunday night’s rally in Portland followed a wild day Saturday in Seattle, where Sanders's well-attended evening rally came just hours after he left another stage in the city where a small group of protesters aligned with the Black Lives Matter movement took the microphone from him. Sanders was scheduled to be the last speaker at that event, attended by several thousand people, at a park. He wound up not speaking.

[Protesters drove Bernie Sanders from one Seattle stage. At his next stop, 15,000 people showed.]

Sanders’s newly hired press secretary, Symone Sanders, an African American woman, warned the crowd before Sanders took the stage in Portland of the possibility that his event could be a disruption there, too. She told the crowd that Sanders was about bringing people together and urged them to chant, “We Stand Together” if protesters took the stage. But that didn't happen.