Yep. There are actually lots of socialist candidates running in local and downballot elections. The DSA, as an example, had around an 86% win rate in the 2022 cycle and conditions are looking favorable to keep the snowball rolling. It's just that the overwhelming majority of these races aren't high profile like Mamdani's was, so you don't hear much about them.

DSA is pretty big despite the establishment's refusal to acknowledge their existence. Most of the DemSoc candidates getting elected (Mamdani included) are DSA-affiliated or endorsed.