It's entirely possible for two opposing sides in a polarized polity to both employ a populist strategy. How you'd see that happening is that the two sides would deliberately exclude moderates and centrists.
It was more obvious in 2020 (with a less complicated, more policy-driven primary) that tons of Democratic primary voters don't want Medicare For All, and that the story as Bernie had told it didn't match the reality on the ground of differing policy goals even within the party's constituents.
Which is exactly what's happening lately.
As Manchin said: "The bottom line is — will the middle speak up? Does the middle have a voice?"
You didn't hear that Sinema left the party? And Manchin is considering leaving it?
That's what I was referring to when I said they were (or at least felt) excluded from the party.