Although Mr. Sanders, as a self-described democratic socialist, has a vision for America that is distinct from the economic system in the former Soviet Union, the word “socialist” was enough to provoke anxiety in Ms. Lazareva.

Image Tom Weaver shows his support for Bernie Sanders’s candidacy with a sticker on his guitar case. Credit... Kirsten Luce for The New York Times

She was unmoved. “Everyone will be hungry, everyone will be poor,” she said. “If it will be Sanders, we will have the same here. Everybody who comes from a communist country, Russians, Eastern Europeans, even Latinos from Cuba, feel this way. When you know what will happen, when you see it — you’re Republican.”

In the apartment directly above her tidy unit, three friends — Tom Weaver, 18; Morgan McIlvain, 18; and Pavel Trofimov, 27 — had just finished eating lunch on their couch. This year would be Mr. Weaver’s first time voting, and, as the sticker of the senator with the Einstein hairdo on his guitar case indicated, he was a Sanders man. He became a supporter, he said, after an online quiz told him that his values and those of the man who grew up a few floors below were aligned.

“It’s empowering to be able to have a say,” he said.

It did not surprise the roommates that a lofty political figure could have roots in an apartment as modest as theirs. “I think a Bernie could come from anywhere — Manhattan, Queens, Bronx, anywhere else,” said Mr. Weaver, clutching his guitar case. “It doesn’t matter where you grow up. It’s the beliefs that you hold, the morals you have.”

Mr. Sanders moved out of the building in the 1950s, around the time he left Brooklyn College. Such humble beginnings might help keep a candidate humble, said Mr. Trofimov, who grew up shuttling from one foster home to another. “All it really comes down to is where you’re from,” he said. “If you’re brought up with nothing but talking to your neighbors and getting to know your community, I think it’s different. You’re more in tune with the people,” he said, while sweeping the living-room floor. Was that a vote, then, for Mr. Sanders?

“I don’t vote,” he said. “I think all politicians are crooks.”

Riding around on his bike outside 1525, where he lives, Boris Ganelin, 62, an engineer, said Mr. Sanders’s socialist philosophy was distasteful to him as a Ukrainian immigrant, but he said he was at a loss about whom he might support.