Virtually non-existent right now in my opinion. But I don't think for one second that established, mainstream Democrats are going to just accept these results. For sure there will be some sort of strong independent candidate that will have the backing of not only the, let's call it for now, "Cuomo wing" of Democrats but also national Republican support.
For an example of what I think they will be attempting, see Buffalo 2021:
https://en.m.wikipedia.org/wiki/2021_Buffalo_mayoral_election
However, if Mamdani does win the general election I think not even Democrats would be stupid enough to not accept that this is their path forward, and we will begin to see a shift nationally as we did with Trump. Of course, they could just be retarded and go down in flames sabotaging themselves as well, but it's impossible to fight against the turnout we saw today if it gets repeated.
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And this is why I keep saying this. Pollsters again got it wrong for this same reason.