Despite what Sinatra would have us believe, if you can make it in New York it doesn't mean you'll make it in the mid west or any of the purple states. (Democrats haven't had a vote share lower than 65% since the 00s I think)
Yes, a record number came out to support him but almost as many came out to support anyone but him :(
My hope is that for all the naysaying, Mamdani turns out to be a technocrat in the Sewer Socialist model and shows the country socialism ain't so scary. The whole "laboratories of democracy" in action.
Counterpoint
Local NYC elections aren't nearly as universally blue as it's national elections, lots of conservative constituencies. This city's self-harm history includes Michael Bloomberg, Eric Adams, and Rudy fucking Giuliani.
It's the finance capital of the world.
The majority of national news media had their machine trained against him for months.
He was up against the Cuomo political aristocracy.
By New York standards, this was a landslide.