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Tiffany Cabán’s apparent victory in the Queens district attorney primary last week seemed like an insurgent triumph, the culmination of a long-shot progressive campaign that drew national attention and proved a new political era in New York.

But by this week, it was clear that the topsy-turvy contest has served another purpose: It has escalated hostilities among the state’s Democrats, spurring accusations of voter suppression and suggestions of conspiracies.

Ms. Cabán’s supporters have accused Democratic officials of throwing out ballots for their candidate, allowing Melinda Katz, the establishment favorite, to gain a 20-vote lead. A state senator, Alessandra Biaggi, suggested illegality was at play, writing on Twitter that “stealing elections is definitely the sign of a real leader.”

Shaun King, a prominent activist, also accused the Queens Democratic machine of stealing the election from Ms. Cabán, and claimed that he had spoken to unnamed officials who told him that more than 1,000 affidavit votes for Ms. Cabán had been thrown out.