Small quibble, it's just a point I'd like to make, don't see it represented here much:
"The truth is that the blame belongs to conservatives. It's been long known that people will vote for a real Republican than a Democrat trying to sound like one."
So I think this is a myth. It's long been apparent that people will actually support and vote for a Dem who positions themselves just to the left of the Republican they are running against. It's the slightly better lessor of two evils thing. If people always chose the real Republican rather than a Dem who supports their policies, the whole third way would have collapsed from unelectability.
Sadly, enabled by the "crazy" right-wing, the third way strategy of getting a lot of corporate money, using it to setup a a formidable campaign machine, claim the "center" while punching the left to establish your cred, is often a successful electoral strategy. Fake Republicans running as Dems can and do get elected. Many people think they're doing something a little better by voting for the Dem corporatist rather than for the Republican corporatist, and there's some truth in that.
The problem isn't that it's a failed electoral strategy, the problem is that when these candidates win, they don't represent us, they represent their large campaign donors, the corporations. Ultimately it does our party, and our citizens, great harm. The policies these corporatist Dems get behind taints our party in the eyes of the electorate, they think Dems are the same kind of crooks as Republicans, and perhaps our reps are a little better but the people for the most part have it right, most of our elected Dems are selling us out in the same way the Republicans are, as directed by the oligarchs that support the whole rotten machine.
What we really need to be looking at is how to win elections without corporate money. Running on policies that actually help the average person, speaking truth to power, doing it like Bernie does, that can make up for some of the advantage the better funded corporatists have. We should be exploring mechanisms to help candidates overcome the huge obstacles they face in elections. Money is a powerful thing, but there are other sources of power, such as truth and sincerity. With the internet, there should be ways to amplify and raise awareness about good candidates who are going up against the beast.
Your final statement, about the left's impotence despite being correct on policy, is dead on, and has been for a long time. We only matter when someone wants to blame us. The corporations have created an entire culture of superficial values, consumerism, conformity, glamor, violence, selfishness, and greed. Their media outlets are incredibly powerful in doing so. The left has nothing comparable, left out.
What we do have is a lot of people in pain worried about their future, and we have the truth that our policies are what is needed to address our problems. There's intrinsic power in that. But we have to learn to win elections without corporate money in order to reclaim our party and restore its good name.
Roughly half of Obama's 2008 campaign funds came from small donors. So, when he got into office, did he dance with us, or the corporations? Obviously the corporations. The half of the money coming from small donors was for the most part not aggregated, so as far as leveraging policies from the president, it carried little more weight than the average size of those donations, which was quite small. Besides, as the third way types will tell you in a candid moment, "where are they (the left) going to go?" We'll see the same thing if Hillary is elected. With no credible threat on the left flank, the people are ignored, mostly without consequence for the corporate politician. That's why something like Occupy was so important, and why it was so brutally crushed.
The corporations who wrote huge multi-million dollar checks were the ones Obama listened to (although I think their world-view for the most part aligns with his own). These people have specific legislative agendas their money supports, and they have a direct line to the elected politicians they "bought". One wrong move, and their support vanishes, they'll take their money to the other party, or they'll destroy the politician some other, more immediate way. Small Mom and Pop donors or their proxies in various NGO's aren't even allowed in the room. We get lip service, they (the corporate donors) get legislation.
Is aggregation of small donations the answer? It could help, so long as the aggregator is 100% representing the people rather than some interest of its own. A credible threat of upheaval or revolution would also get their attention. A serious and determined third party on the left would also help. Personally I favor working within the party, possibly using a far-left socialist wing under the Democratic Party tent, whose candidates would be forbidden from taking corporate money. Whatever the answer is, it doesn't involve electing candidates who share and validate the world-view of the corporatists and the Republicans.