They didn’t do anything to Bernie Sanders; the big-tent party moved rightward after Raegan but it’s progressive wing didn’t break off. His placement in both primaries reflects that.

Disclaimer: I’m not an American, so I might be simplifying or not getting something right.

EDIT: looking at your comment again, I could understand cynicism about the Democratic/Republican political machines, but I don’t necessarily equate that to something like Iran’s Supreme Leader.