For the reds, Mamdani is all the redscare, islamophobe and racist things they've been told to hate. For the blues, he's some sort of saviour and proof that democracy in America can actually work as intended, and isn't just something between entertainment and PR. You need a protagonist and an antagonist to build a narrative, after all. But the system never worked in your favour and nobody in power has any morals or virtue (else they'd just get taken out, lol, you think the CIA is above that?). And the population either doesn't care or doesn't notice because they themselves are iffy, their cultural baggage came with everything but belief in objective morality and virtuous duty to the rest of humanity. The "all that matters is the bag and my pleasure; death, rape and pillaging is acceptable if I get what I want" (how do you think the country was created? How do you think they gained and maintain their wealth?! It doesn't matter if you say you're A when all you do is B, stop lying to yourselves, please) culture will never breed respectable people in enough quantities, if they happen to exist there its by accident, and none will reach a position of power.
They tried dark skin with Obama but they can't do that again, then they tried white female but she was an obvious see you next Tuesday, so they tried pushing AOC cause she's a bit more personable and attractive while being brown but she's not that popular either so now they're going with brown "Muslim" man, that's all.