“There is a lot of energy among progressive white folks here,” Mr. Griffith said. “And there are black folks who are sort of waving their hands to say, ‘Yeah, I’m feeling the Bern, I’m going to support.’ But, let me not overstate it.”

Like many Brooklynites interviewed for this article, Mr. Griffith said he had not seen much effort from either candidate in his neighborhood. “When I don’t see a lot of evidence of either campaign going on, that does not bode well for Bernie Sanders,” he said. “It is a much better sign for Hillary Clinton, because on some level she is in a position to take black votes for granted and he is not.”

But Sanders supporters have been self-organizing for more than seven months, according to Karthik Ganapathy, a Sanders spokesman based in Brooklyn, who also explained that the campaign expected to do well in Crown Heights, Park Slope and Bushwick. “The mistake there would be to assume that those are the only places that we are going to do well,” Mr. Ganapathy added.

Olivia Flood, 24, who lives in Flatbush and works at an entertainment company, said she had helped collect signatures to get Mr. Sanders on the ballot because supporting Mr. Sanders in Brooklyn meant acknowledging the easily seen economic differences in the borough. “You can’t live in a bubble in Brooklyn,” she said. “You step in one neighborhood, you’ve got a completely different way of life. Then, you step over the line and it’s another way of life.”

A Long Island native who recently moved to the borough, Ms. Flood said she hoped other new residents would come out to support Mr. Sanders. “We can advocate for him and that’s important,” she said.

Lisa Flythe of Park Slope is also among those advocates. She started volunteering in December; three weeks ago, she spent about three days canvassing on Flatbush Avenue, a main Brooklyn thoroughfare. The experience forced her to confront a now familiar issue. “The biggest problem is that people didn’t know who he was,” she said.

Mr. Sanders’s advisers say they feel confident the senator can overcome obstacles, as he has in other places.

“We are underdogs,” Mr. Ganapathy said. “We are in a familiar position. But that is just where we like to be.”