Part of what made Mamdani so successful during his campaign was that younger voters perceived him to be authentic on social media, says Jane Hall, communications professor at American University.

"You don't have to be young to be able to do it, but I think you have to be seen as being authentic and speaking to what people care about in a way that is hip and makes people want to be on the bandwagon," Prof Hall said.

Mamdani's critics have argued that he does not have enough experience to lead the largest US city effectively.

Trump has tried to paint him as radical, repeatedly calling him a communist, though Mamdani has frequently rejected that label. The president also has threatened to withhold federal funds from a Mamdani administration.

After declaring victory in the mayoral race, Mamdani addressed the president directly: "Donald Trump, since I know you're watching, I have four words for you: Turn the volume up. To get to any of us, you will have to get through all of us."

Trump promptly posted on social media: "…AND SO IT BEGINS!"

Andres Bernal, former policy adviser to New York Representative Alexandria Ocasio-Cortez, says Democrats can learn from Mamdani's ability to connect with people.

"Today's Republicans shape public discourse and they try to shape political consciousness in this country," Bernal argued. "While Democrats kind of just assume that people have fixed beliefs and they look at polls and say, okay, how do we match what we say to what we think people believe?"