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.
Wait until they see his results, if the right doesn't interfere. When FDR got in they couldn't get him out because he was so wildly popular. Also, Bernie Sanders was wildly popular with the people, but no so much with corporate Dems.