First,why does he believe this? The progressives are all from safe districts. They can very safely play hardball for progressive values. They aren't going to lose their seats.
Second, the progressives (as you so clearly point out) couldn't lose. Because they were ALWAYS going to get the baseline Medicaid expansion. They would have fought for getting that through reconciliation and they would have won and their stakeholders would have applauded that victory.
Third, (and somewhat less clearly) I think it still comes back to defining who the "counterparty" is. Personally, I can't think of a counterparty in this negotiation (Republicans, Blue Dogs or Obama) who shouldn't have understood points one and two. But Silver seems to think the "counterparty" (undefined) would not understand these points.
I think the problem with the progressives is the same problem that Silver has - they do not have in their minds a clear definition of who the "counterparty" is and they have, therefore, created some imaginary counterparty who they have imbued with superpowers. Or possibly who they have imbued with such stupidity that they think they are unable to read the tealeaves.
If the Progressives had kept their eye on the ball from day one they would have (i)realized that the only counterparties who mattered to THEM in this negotiation were Obama and a few non-progressive Democrats, (ii)Obama and the non-progressive Democrats weren't stupid and would realize the progressives were from safe districts, and (iii) the progressives were always going to be able to claim victory on the baseline progressive goal of expanding Medicaid.
Once you realize that, the only question is how long you string along the non-progressive democrats in the process to get them to the point where THEY can't afford not to pass a bill that they never wanted in the first place. There is always that point. At some point a party who is otherwise lukewarm to the whole idea has so much time and money and effort and emotion invested in the process that THEY can't afford to go back to THEIR stakeholders and explain why they put so much time and money and effort and emotion into a deal that they then killed claiming they never wanted it in the first place. Explaining becomes harder than just getting it done. It always reaches that point. You just have to be patient.
As the unions were.
Great analysis.
Speaking for me only