Not being in NYC, I can’t say how many people are thinking, “I don’t really want to vote for a socialist, and I don’t like the current mayor, but I can’t vote for Cuomo because of the harassment charges, so I’ll vote for the socialist instead.”
This race has gotten a lot of attention, both for its national political implications and from a real estate perspective, but in what I’ve read the harassment issue hasn’t really come up (again, not to imply it's playing no role).
The Party already knew this about him. I’m not sure if they didn’t think it would hurt him, or just felt they didn’t have any better options.