The talkative part is over as soon as the election result is declared. The difficulty sets in and it can show. In other large cities, a new Mayor discovers that just a part of their platform is not possible. In New York’s case it may be they discover all of Mamdani’s key points are unlikely to work out well.
There’s a particular relaxation of the rules when it comes to a Left candidate in America. People recognise that the policies are unsound and not workable but give extra room for effort. It looks good to have somebody that’s enthusiastic about the role at least. 
In time, however, to make the office professional again, there has to be a search for answers. This leads to a drafting in of local experts to help make the plans that will benefit the area more solidly. These replace the goals made by crowds at their respective kitchen tables.
In New York City, there’s usually a reckoning soon after an election with the reality of not just statistics but public opinion. There’s a wide variety of interest groups in the City that feel alarm over the level of decay that’s taken place so far. This is a difficult front to have to overcome and cannot be won popularly.
While Mamdani has a politically motivated constituency of his own, the groups are very wealthy and heavily invested in the built environment. An issue like rent control, which is really a matter of who lives where, is not a battle that he can win easily. It’s also already coveted by social experts who look at it religiously.
If he’s a diplomat, he’ll provide clarity between all the competing groups in an important urban space. His likely ethic is to hedge with charity but align with reality. This will bring a modicum of change, but not reassure most renters who need their monthly payment to be affordable. It’s also not something that can last fifty years into the future.
Magic Mamdani may be able to work some spells and get people to agree behind closed doors, but it’ll be a far cry from his rhetoric during the campaign. The lesson of the Left continues in one of the biggest fields of play in the world. It’s a test of democracy, but also of people’s patience, and such wrangling as this can’t last forever before the real troubles come.
