For me Sanders is in much the same camp as Trump, albeit he's infinitely more likeable. The reason I lump them (and to a large extent Corbyn) together is that they can largely attribute their popularity to proposing schemes that sound great but are largely unworkable. It's an old adage that it's best to under-promise and over-deliver, but populist politicians are the exact opposite, as we've seen with the likes of Syriza and the mess we're in with Brexit at the moment, where most of the promises that got them where they are, are unlikely to be kept.
I'd much rather a politician who was honest with the electorate and ensured pledges had at least some attachment to reality, even if that makes them less grandiose and tub thumping.
Do you really think Sanders was tub thumping just to get elected? Not playing dirty surely showed he wouldn't follow the usual tactics just to get the nomination, and as such would that not suggest he was genuine in his beliefs and in what he could do? Rather than just say whatever all the time like Trump.
Perhaps Sanders point was....this is how it should be. Your point about unworkable schemes is fair enough in the current climate and system, but perhaps what Sanders was saying is this is how things should be and the system should change to make these things workable. Considering the large flaws in most governments in the US for many years, what cost an idealist who would try to make a proper change?
If we always only play within the current system and rules nothing can move forward. Which is dangerous in politics when for so many it seems the system is rigged. The reality that you feel the pledges should be attached to is perhaps not the preferred one for many people. Even if ultimately such a President might hit a brick wall in his efforts it would be a start, no?
To be honest I am far from an expert in this area so my point might be a little superficial, but I'd be interested to hear your thoughts.