He voted on a resolution calling for the extradition of Assata Shakur.
It's quite simple. You can't be a socialist and call for the imprisonment of a black nationalist freedom fighter.
If Sanders gets elected, making him the oldest president in the history of the US, and happens to get universal health care through, that's great.
But he isn't a socialist. He's a left-wing imperialist. It doesn't matter what his positions are. When you are placed in the leadership seat of the Amerikkkan project, you are a part of the machine. And either you continue putting that machine to work, or you're booted. And the work of that machine is imperialism, it's bloody massacres and coups. It's drone strikes and the body regulation of the global working class.
Socialists have no business trying to do ANYTHING with the democratic party. The DP has proven itself milquetoast and afraid of leadership. It's a center-right variant of neoliberalism. There is nothing worthwhile in that piece of shit. It's rotten and has proven itself the death of movements since the 1960s. The DP is the graveyard of the civil rights movements, the latino working class movements in the 60s/70s, the anti-war movement, the LGBT movement, the undocumented struggles of last decade and more.
Socialists have the goal of creating proletarian power. We care not for the bourgeois state, which we aim to smash and destroy. We aim to create a proletarian state, which is fundamentally different in nature from the bourgeois state. The proletarian state is a state, in that it is organized class-power. Beyond this, its features are entirely different. We use that proletarian state to institute and solidify, concretize, socialist relations. We do not make socialism by voting in bourgeois elections. We do not make socialism by wasting our energy with the democratic party.