New York's new mayor, Zohran Mamdani, has vowed not to water down his ambitious agenda as he promised a new era for the city during an impassioned inauguration address.
The 34-year-old was sworn into the mayoralty outside City Hall by one of his political idols, left-wing senator Bernie Sanders.
The public ceremony in sub-zero temperatures followed a lower-key midnight swearing-in at a subway station.
"I was elected as a democratic socialist and I will govern as a democratic socialist," Mr Mamdani told his supporters.
"I will not abandon my principles for fear of being deemed radical."
Mr Mamdani comes into power with a pledge to redistribute the city's wealth and make life affordable in America's most famously unaffordable metropolis.
His detractors see him as radical and dangerous, and his doubters say his vision is impossibly far-reaching.
But his fans are hoping for big things, and many believe he could produce a blueprint for transformative city governance elsewhere in the US and abroad.
"People want so much from this guy," University of Virginia public policy researcher Nicole West Bassoff said.
In his inauguration speech, Mr Mamdani said New York had for too long been "accepting mediocrity from those who serve the public".
"In writing this address, I have been told that this is the occasion to reset expectations, that I should use this opportunity to encourage the people of New York to ask for little and expect even less," he said.
"I will do no such thing. The only expectation I seek to reset is that of small expectations.
"Beginning today, we will govern expansively and audaciously. We may not always succeed, but never will we be accused of lacking the courage to try."
Senator Sanders said his protegee had achieved the biggest political upset in modern American history after taking on "the Democratic establishment, the Republican establishment, the president of the United States and some enormously wealthy oligarchs".
But he warned that the groundswell of grassroots forces that propelled him to power must now be maintained for him to succeed in office.
"Running a great and winning campaign was extremely difficult," Senator Sanders said.
"But governing a city of 8 million people, with all of its complexities and all of the problems that Zohran is inheriting, will be even harder."
Spanner in the works
Mr Mamdani easily won the city's mayoral race in November.
His headline promises included free childcare, free city buses, and freezing the rents on the city's 1 million rent-stabilised apartments.
But he faces many opposing forces, including those listed by Senator Sanders. And there are plenty of sceptics who see his agenda as unachievable — even over the two-term, eight-year timeframe Mr Mamdani has given himself.
Free universal childcare, currently offered by no major US city, will cost billions and need ongoing support and investment from the state government.
Free buses will also require the backing of the state, where the governor and other powerful players have expressed reservations about lost revenue.
And rent freezes can only be decided by the city's Rent Guidelines Board, whose members are appointed by the mayor but must follow a formal process to arrive at their decisions.
Eric Adams, who Mr Mamdani replaced, may have thrown an early spanner in the works on his way out.
He appointed several new rental board members in the final month of his mayoralty, and they will likely not be easy for Mr Mamdani to immediately replace.
Most board members' terms will expire while Mr Mamdani is in office, which means he will have the chance to eventually stack the board in his favour.
But Mr Adams's move is an early example of the pushback forces the new mayor will face as entrenched interests work to frustrate his agenda.
Forging alliances
Whether Mr Mamdani succeeds or fails depends not only on bodies such as the Rent Guidelines Board.
Mr Mamdani will need the support of the governor's office and the state parliament — both of which are controlled by Democrats — not just to implement his promises, but also to raise the funds to pay for them.
"The evidence so far suggests that he's doing a really good job of working with the governor to try to fund some of this," Harvard University public policy professor Justin de Benedictis-Kessner said.
"Of course, the city can't raise and lower tax revenue on its own, so he's going need that partnership."
Mr Mamdani's key wish is for the state to take up his plan to increase taxes for corporations and the top 1 per cent of earners.
Governor Kathy Hochul, who is up for re-election this year, has backed big parts of the mayor's agenda — particularly free childcare, which she has made a key priority of her own.
She opposes raising income taxes to fund it, but has shown a willingness to talk about raising other taxes instead.
'Decent amount of goodwill'
Mr Mamdani is confident he has the support of the people he needs in Albany, where New York's state government is based.
His election bid won the endorsement of Governor Hochul, Assembly Speaker Carl Heastie and Majority Leader Andrea Stewart-Cousins — seen as the three most powerful players in the state legislature.
"In Albany, it's often spoken about as 'three men in a room'," Mr Mamdani told the Flagrant podcast in October.
"Now, it's two women and a man who are in that room.
"And to have the endorsements of all of them, it's huge and it paves the way for this agenda."
Scholars of New York's history, such as the University of Virginia's Dr Bassoff, point out that the city's mayors and the state's governors often have hostile relationships — even when they hail from the same party.
But Dr Bassoff said Mr Mamdani was entering the mayoralty with a "decent amount of goodwill from the governor".
"The issue that I suspect that we're all watching, and that will be very important within his first two years, is the universal childcare issue," she said.
"And he is, I think, in a good position there as far as having the committed support of the governor."
Trump factor
One of the biggest potential threats to Mr Mamdani's agenda looks to have been mitigated — for now, at least.
Donald Trump had strongly opposed Mr Mamdani's mayoral campaign, and he threatened to withhold federal funds from New Yorkers if they elected him.
However, when the pair met at the White House after Mr Mamdani's thumping victory, Mr Trump said: "I expect to be helping him, not hurting him."
"A big help, because I want New York City to be great," Mr Trump said during an unexpectedly warm joint press conference.
But Mr Trump's relationships with other politicians — both friend and foe — are notoriously volatile, and federal funding cuts remain a live threat.
The Trump administration has shown a willingness to punish New York in this way before.
In October, during a government shutdown stand-off with Congress's Democratic leaders — who happen to hail from New York — the White House froze billions in funds for New York rail projects.
Even if he does not directly interfere in city affairs, Mr Trump's heavy influence on American politics will be inescapable in the US's biggest city.
But Dr Bassoff said Mr Mamdani represented a politician who appeared able to successfully "do politics in the Trump era" — and not only because of his ability to forge partnerships with unnatural allies.
"Doing politics in the Trump era so far has basically meant ceding the conversation to Trump, continuing to give him centrestage," she said.
"And so someone who can compete on that stage and actually steal the headlines for themselves, I think that's another thing people are looking for.
"The idea that a mayor could be the someone to do that and actually bring our attention to other things — it's kind of incredible."
'Ample precedent'
Despite the clear challenges ahead, the experts who spoke to the ABC expressed optimism about Mr Mamdani's chances of success.
Columbia University political historian Kim Phillips-Fein said his headline promises were not as radical as many people had framed them.
"There's ample precedent for all of these within the city's history," Professor Phillips-Fein said, pointing to past examples like successful rent regulation and expansions of early childhood education.
"People have sometimes described these [promises] as being such dramatic things that have never been tried before, and that's just not true."
While there are "many obvious obstacles" — including a Republican president and party that hates a lot of his agenda, a Democratic Party internally divided over its own direction, New York's entrenched economic interests and a hostile right-wing tabloid press — Professor Phillips-Fein sees "great cause for hope" for Mr Mamdani.
"But this really is a time of uncertainty," she said.
"Much will depend upon the organising effort and the forces that brought him into office in the first place, the way that they are able to keep organising and generating support for deeper political change."
Professor de Benedictis-Kessner said that while deep polarisation and divisive party politics often impeded positive progress at other levels of government, America's city governments were generally functioning well.
"I'm really optimistic about the chances for local government to do big things because if anyone can accomplish those kinds of things in government these days, it's definitely city governments."
