Thats the problem though...
Throwing in with the Green Party would be disastrous given the anti-democratic FPTP electoral structure of the States as they lack the access, resources, exposure and infrastructure to capture office, and short of subsuming the Democrats, would present a net liability as a spoiler. Progressives know this, and the vast majority of people who would otherwise be attracted to them know this, which is largely why they, and the Libertarians as their conservative counterpart, won't ever gain real traction. It has nothing to do with their views and stances, but the way governments are elected and the reality of the resources involved.
Everyone talks campaign finance reform. Every time something gets passed, it gets gutted in the federal court system. Of course that will only be worse today because the Republicans now get 4 years of nominations.
Right, it's called Buckley v Valeo, and it's why a constitutional amendment is necessary such that money is explicitly no longer considered speech so campaign finance reform can be meaningful.
Single Payer is a political impossibility. ...
The argument to moderation fallacy is just that; it's the polling and zeitgeist that matters, not what one perceives as being within the Overton Window of acceptability per his confirmation biases. For all the bluster about Bernie's ideas being wildly radical and unworkable, the vast majority had and continue to have overwhelming support; going left would win the election, not keeping to the centre (which is largely abandoned and displaced to the left and right in times of frustration when populism is in vogue anyways). There was no patience or appetite for centre corporatism this election cycle, or even the bull**** right wing style populism Trump offered as voter turn out proved, as did the rust belt flip.
That having been said, I agree that passing popular ideas and legislation such as what Bernie proposes would be politically difficult, but that is primarily due to top down opposition per the marriage of private money with public office, and the associated lobbying and applied weight of rich and powerful donors, not because those ideas wouldn't sell with the public. However, difficult is not impossible, and despite the considerable array of obstacles set against it, with enough people like Bernie, and the Justice Democrats following his example that are making their way through the Dem primaries, it can be done.
Beyond all this, I do the best investment of time and energy, pound for pound for anyone who cares about an integral, representative government, is getting through a constitutional amendment to definitively insulate money from politics, including spending caps, and its indirect forms such as lobbying, SuperPACs, independent advertising spending, and so on, so that such policy isn't so impossibly difficult to pass because it would no longer need to withstand the gauntlet of a bought Congress and Senate laden in vested interests.
Why not blame the Democrats who essentially squandered their 2 year House and Senate majority? There's a reason midterms flipped; every effect has its cause. Again, you can't place all or even the majority of blame on the voters; politicians first and foremost have to earn the confidence of the people, not the inverse.
As to corporatism. I don't like candidates being beholden to big corporate lobbyists either. However, here is the problem...
Outside of Perez' embarrassing semi-coherent groping rambles about transparency in response to allegations of DNC rigging, and maybe one of Trump's public addresses, this is probably the most obtuse thing I've seen within a week. So corporatism and corruption is a bad thing but if you happen to work for a company then you'll end up thinking it's a good thing, but wait, look over there, the Republicans are worse! That about the gist of it?
You're not wrong about the Republicans being worse, but at the same time being an apologist for Dem corporatism is the wrong policy. The subversion of political office and legislation by private money is terrible no matter who does it and no matter their reason, something to be despised and at the first opportunity rectified, never ignored, minimized or glossed over. Yes, it shouldn't mean that you vote 3rd party or GOP if the alternative is truly much worse per Hillary and Trump, but that much is understood and obvious.
In general, incrementalism, or at minimum, the active pursuit of incrementalism is a proven failure, as is centrism (or its American incarnation) and status quo ideas in this political climate, losing to Donald Trump of all people. The establishment Dems have no leg to stand on outside of their funding advantage and incumbency, having lost in every way it is possible to lose. Your prescription is wrong and dangerous precisely for that reason.
