Let's take a look at this "changing what can be." How exactly is electing Sanders supposed to do that, other than through some Sanders magic wand?
DNC members would be more than happy to talk about Medicare for all...if you, Sanders, anybody had the slightest idea how to go about making it happen. So...other than "elect Sanders and see the magic" WTH do you got? I'm listening. Take your shot.
IF the Democrats get control of the senate it is going to be razor thin. So unless your great plan involves "first, shoot all the Republicans" it is DEAD. DOA. Finished.
Now, somewhere in this thread I suggested, since I too would like to see Medicare for all, that the only way I see to get there is squeeze in a public option access to medicare, then hold power long enough for it to drive out the private sector competitors without the GOP getting back in and fornicating all over it. Undoubtedly that doesn't sound magical enough or provide the instant gratification that Sanders promises, but it does have the benefit of being at least marginally realistic.
And just in case...no, I didn't think that up on my own, that is bog standard policy throughout the Democratic party.