What middle? All this bullshit about having to adhere to some strawman voter, that is super informed, can't be swayed by debates, arguments, charisma, and knows exactly where this mysterious border is, over which they SHANT CROSS, is a complete lie. Voters are uninformed AF. It's all about messaging, charisma, if they trust you, do others support you, and so on. It's a matter of psychology. and that is something that's unpredictable. With the right combination of appeals you can have voters for anything really.
There's a case to be made that a message such as Bernie's - where you just straight up counter the narrative of the "socialism is bad" bullshit, works better to get voters to your side, than some middling "yeah sure socialism is bad, let's do this minor thing tho", when you have the opposition making much grander appeals. You can't have the same strength of appeal as the Republicans, when all you have is incrementalism or maintaining the status quo.