"electability" was always a sham. It is exclusively used by millionaire news pundits and NYT writers to tell primary voters not to vote for the candidate with the policy that immediately improves the material conditions of the most people because of an imaginary cohort of "centrists" and "moderate republicans" who are terrified of anything good like free healthcare, child care, college, rent-control, and taxes on billionaires, but will totally vote for the version of those policies that will help nobody.

I agree but you have to focus on outcomes. Does endorsing him help or harm him? Does endorsing him help or harm themselves? The answer to these questions might very well be "I don't know".

If some general polls shine a big awesome light on Mamdani being the best possible candidate to defeat the Republican nominee, then hopefully that is more than enough reason for these few Democrats to fall in line behind him. If he polls at like 25%, it's going to start being time to look at other options.