Mamdani celebrates victory in 'reborn' New York City

New York City mayor-elect Zohran Mamdani addressed President Donald Trump directly during this victory speech.

"Donald Trump, since I know you're watching. Four words for you: Turn the volume up," Mamdani said to deafening cheers.

Mamdani has been a high-profile target of Trump -- who has branded the Democratic Socialist as a "communist" and vowed political retribution.

Mamdani, who was born in Uganda, vowed to protect immigrants, saying, "New York will remain a city of immigrants, a city built by immigrants, and as of tonight, led by immigrants."

"So hear me, President Trump, when I say this: To get to any of us, you will have to get through all of us," he said to applause.

During Mamdani's speech, Trump -- who threatened to slash federal funding to New York City if Mamdani won -- posted on social media, "…AND SO IT BEGINS!"

After thanking his volunteers who "built this campaign into an unstoppable force," New York City mayor-elect Zohran Mamdani urged the city to "breathe this moment in."

"We have held our breath for longer than we know. We have held it in anticipation of defeat. Held it because the air has been knocked out of our lungs too many times to count. Held it because we cannot afford to exhale," he said. "Thanks to all of those who sacrificed so much, we are breathing in the air of a city that has been reborn."

He spoke of his campaign promises to freeze rent for more than 2 million rent-stabilized tenants, make buses free and deliver universal child care, calling it "the most ambitious agenda to tackle the cost-of-living crisis" in the city.

"Years from now, may our only regret be that this day took so long to come," he said. "This new age will be one of relentless improvement."

New York City mayor-elect Zohran Mamdani said New Yorkers have "toppled a political dynasty" during his victory speech following former New York Gov. Andrew Cuomo's concession.

"I wish Andrew Cuomo only the best in private life," Mamdani said to cheers, adding that tonight will be the "final time I utter his name as we turn the page on a politics that abandons the many and answers only to a few."

Mamdani began his victory speech with a quote from socialist Eugene V. Debs, saying, "The sun may have set over our city this evening, but as Eugene Debs once said, 'I can see the dawn of a better day for humanity.'"

As Zohran Mamdani turns from campaigning to governing, a source close to the mayor-elect told ABC News he is intent on reaching out to New Yorkers who did not vote for him and send a strong signal that he plans to be a mayor for all New Yorkers.

That will be a focus of his transition in the coming days and weeks in meetings with civic, political and business leaders, the source said.

He also plans to send a signal to New Yorkers who have concerns about his relative youth and lack of experience with the appointments to his administration, the source told ABC News.

As for the national stage, Mamdani's focus will be on pushing back on Trump's efforts to impose his will on the city, according to the source.

But, the source said, he also recognizes that his victory could offer Democrats a blueprint to win back a "multi-racial and working class" coalition across the country.

-ABC News' Ben Siegel