She stood before a far smaller group of supporters than on election night, the euphoria slowly drained from the moment when victory had seemed assured.

Tiffany Cabán was to be the Next Big Thing in the progressive movement, another candidate emerging from anonymity to upset an entrenched Democrat . She vowed to not merely reform the district attorney’s office in Queens, but to upend it.

Then just like that, her moment — along with her roughly 1,100-vote lead on primary night — disappeared after a count of paper ballots and then a lengthy recount, leaving her to deliver a concession speech last week that was at once anticlimactic and hopeful.

“I said stages like this were not made or built for people like me. And that has changed,” Ms. Cabán, a 32-year-old public defender, said last Monday night. “We build the stages. We create the spaces. We create movements. We drive change.”