He let them do it. Put up no protest and then gave them his support after they fought him with their whole apparatus.

He’s also a Zionist, weak tea when it comes to policy, and completely incapable as an organizer, throwing away his network twice after losing. He was always a compromise candidate at best from a left perspective and is only perceived as particularly left wing in comparison to the duopoly status quo of proud neoliberal racist vs. false pretense neoliberal racist.