The problem isn't really anyone here though, it's the Electoral College. From a purely popular vote standpoint pretty much anything we want to do is popular enough with the broad American electorate. However, it's unpopular enough, with enough people in the right places that it makes it moot. You'll likely never see a Democratic Presidential nominee win the EC and yet lose the popular vote, yet it's happened twice in my lifetime the other way around.
In reality, the things that would be the most beneficial things for us to do would be to grant Washington DC and our territories Statehood and to try and pass the National Popular Vote Interstate Compact in every State.
And, to be real here, it would help if Progressives showed the way, you listed a lot of gripes about California, well, shit, if you can't show the country how to do Progressivism right in California why would a Red State or a swing State think it's a great idea? And I don't mean to shit on Cali, you guys do a lot of good things, but, as one of the larger economies in the country, nay, world, almost all of those problems are just as much in your reach via the State apparatus as they'd be from the Federal. State tuition, that's a local and State issue, health care, regulated by the State, Fires, State and local issue, homelessness, State and local issue, you guys are focused on the sexy Presidential race when California could reasonably tackle most of its' issues on its' own in a way most States couldn't.
If we lose in November I wonder if it'd be better for organizations like the DSA, Our Revolution, Justice Democrats, whoever, to just go ham on one fucking State, try and take the whole thing. Try and build an example, on a smaller scale, what could be done nationally. It's clear that using other countries as examples means nothing to most Americans, take California or some shit, give it great healthcare, tuition free college, proper housing markets and slap America in the face with it.
The incumbent party generally always loses seats in the midterms, the idea of you being more prepared in the second half of your term to pass a major piece of legislation like Medicare for All is unprecedented. Anything you state to happen in your third or fourth year that isn't an Executive Order that you just didn't feel like passing earlier for, reasons I guess, is something you're basically saying won't happen. If you're going to pass M4A it has to be in the first 2 years.