Bonsu Thompson was, by his own admission, an unlikely host for a fund-raiser for Cynthia Nixon’s campaign.

Mr. Thompson, a writer and producer, had never organized an event for a candidate before. Usually, he found politics distasteful. “Folks who know me know that I’m not exactly a political person,” Mr. Thompson told the crowd of roughly 150 people gathered on the Bowery Hotel’s rooftop for the Aug. 1 event.

But if Ms. Nixon is to have any chance of defeating Gov. Andrew M. Cuomo in the Democratic primary on Sept. 13 — as her campaign insists she does, despite poll after poll in which she trails him by gaping margins — it will be because voters like Mr. Thompson became political people.

“Polls are not capturing who the new electorate is,” Ms. Nixon said. “We have a younger, more progressive, more diverse electorate. Those are the people that are going to turn out for me.”