The history of the PPACA and the 1990s "Clintoncare" (which was in most ways further left than the PPACA) issues are instructive here. Same with the attempts to get the public option past Lieberman or the history of the so called "Tea party."
You start to strain reasonable inferences _very_ quickly with counterfactuals of "well if they had just come out EVEN FURTHER LEFT…"
What evidence is there to support that position? Other than vibes, of course.