Imagine that all you ever eat is chicken. You go to the grocery store and see chicken molded into globes and painted red under the sticker “Apples.” And then you see chicken shaped as oblong objects and painted green under the sticker “Cucumbers.” You’ll try all these offerings and realize that it’s all pretty much chicken, with slight variations.
So when somebody asks you, “Would you like to try a cucumber?” obviously you will respond, “Nah, I already tried it and it’s the same old chicken.”
When Sanders calls himself a Socialist, he’s selling you chicken painted green and titled “Cucumber.”