The leftist variety who attack Christians do not practice the religion of Judaism, they’re atheist. Why they’re still considered Jews is something that I don’t quite grasp, yet they are. Observant Jews are for the most part allies.
They are atheist Marxists, but many of them still do Passover Seder and similar things as a matter of tradition and consider their Jewishness to be a main part of their identity. Agreed that the religious ones are more likely to be allies.