The mouthwatering showdown between the Republican and the young Democratic socialist could define the next phase of Trump’s presidency.
Trump has appeared to relish having Mamdani as a foil, branding him a communist, mocking the name of the first Muslim and South Asian to lead America’s largest city, and threatening to cut federal funding for New York City.
But his rival has shown he can play Trump at his own game.
It’s rare for former reality TV star Trump to see himself upstaged, but 34-year-old Mamdani managed it at his victory rally on Tuesday night.
“Donald Trump, since I know you’re watching, I have four words for you – turn the volume up!” he said to huge cheers.
White House press secretary Karoline Leavitt confirmed to reporters travelling with Trump on Air Force One the next day that the president had indeed watched Mamdani speak.
‘Go through all of us’
Trump and Mamdani are, at least partly, enemies with benefits.
Leftist Mamdani used Trump as a bogeyman throughout his mayoral campaign, accusing him of “fascism” and comparing the billionaire property developer to the landlords he says are ripping off New Yorkers.
He has also cannily positioned himself as part of the resistance to a president who has pushed his power to its limits and sent the national guard into Democrat-run cities.
“To get to any of us, you will have to go through all of us,” Mamdani said at the victory rally.
For hapless Democrats who have struggled to find a winning message as Trump has savaged them in recent months, Mamdani represents a long-awaited chance to fight back.
But for many on the right, Trump now has the ideal opponent to bash.
As Republicans nursed their wounds from defeats in New York, Virginia and New Jersey, Trump said in a speech in Miami on Wednesday that Americans now faced a “choice between communism and common sense.”
Trump also blew a dog whistle to the hard right.
“Mandami, whatever the hell his name is,” Trump said in the same speech – deliberately mispronouncing Ugandan-born Mamdani’s surname in the same way he did with his 2024 election rival Kamala Harris.
‘Flashing red lights’
Yet the stakes are far higher than a war of words.
Trump has repeatedly threatened to put New York – his beloved home city – in the federal crosshairs like he has previously with Los Angeles and Chicago.
“If he is a communist, there’s not going to be a lot of activity,” Trump told reporters in the Oval Office on Thursday. “So you wouldn’t need bridges and tunnels and all the different things that were being planned for New York.”
Some allies, meanwhile, fear Trump could be playing with fire by focusing on a man whose rise was propelled by the affordability crisis that is now hurting Republicans in the polls.
“There should be flashing red lights all over” for Trump, former White House strategy guru Steve Bannon told Politico. “People better understand they have a fight on their hands. This guy is a serious guy.”
Both Trump and Mamdani have also indicated they may ultimately be ready to cool things off.
Trump has veered between saying he wants to “make him succeed” because he loves New York and, in the same breath, urging Mamdani to be “a little bit respectful of Washington”.
And Mamdani will be aware that his campaign pledges of free city bus travel, childcare and city-run grocery stores will struggle if Trump cuts federal funding.
“I continue to be interested in having a conversation with President Trump on the ways in which we can work together to serve New Yorkers,” he said on Wednesday.