In the campaign’s closing weeks, Mamdani’s rival, former Gov. Andrew Cuomo, described the race as a central front in a civil war for the Democratic Party. Cuomo and his surrogates desperately caricatured Mamdani as both a woke extremist and an Islamic fundamentalist, making common cause with President Trump and flooding social media with hateful A.I. slop. Mamdani, the obvious front-runner for many months, cut a different profile — looking not like a Manchurian candidate but instead like the embodiment of publicly financed elections, pitching the promise of a new generation’s politics to a disengaged electorate. On election night he took a more strident tone, opening his acceptance speech by quoting Eugene Debs and pointedly picking a fight with Trump.