For myriad reasons Shaun King is not the most reliable of commentators, but I'd encourage you to give this take on the fundamental problem with the Democratic Party moving forward a look. In particular this part at the conclusion is worth thinking about:
Recently, I’ve asked the crowds where I am speaking two key questions about the Democratic Party. The response that I get is always the same – mass laughter or audible frustration.
The first question is, “If I asked you, in just a few sentences, to sum up what specific policies the Democratic Party stands for, what would you say?”
People have no genuine idea. They know some things the party stands against, but it’s genuinely hard to be sure of what they stand for.
The other question is, “What exactly is the strategy of the Democratic Party to take back the government from conservatives across the country?”
That one always gets the most laughs. Nobody has any idea. Not once has somebody stood up and said, “Hey, I know the strategy.” Hell, I don’t know it. I don’t think one exists. Whatever the strategy was this past election, it didn’t work either. And again, I don’t just mean in the presidential election. Democrats lost all over the place in national, state, and local elections.
I think this is as good a way to sum up the current problems on the left as any – twenty years into the experiment in forever moving toward the middle to "peel off moderate Republicans," nobody can really tell you what the Democratic Party stands for anymore. Republican Lite and the post-Reagan death of actual liberalism have left the party without any meaningful identity other than "Not the Republicans" and the GOP has managed to brand a party that is barely left of center on most issues (and to the right of it on a few) as some sort of radical Marxist death cult. That was a problem before 2016 and it's a problem now.
Ask people what the GOP stands for and they will say small government and low taxes. Now, you and I know that they don't actually stand for small government in practice; they merely want the government to be very big, expensive, and intrusive in a way that suits their preferences. But the point is that people can tell you what the Republican Party is about. They can tell you what the brand name means.
Try to explain what the Democratic Party stands for using any amount of words, from a short slogan to a healthy paragraph, and you'll find that you can't. "Liberal on social issues" is about the clearest, most concise true statement I could come up with, and even that is a comparatively recent development. Ten years ago they were still talking about Civil Unions, the most prominent example of their inability to show leadership on these issues and instead to wait until they're absolutely, 100% positive that a majority of the public will support them before embracing any changes.
Economically and in terms of foreign policy, they've signed off on so much of the Republican agenda since 1990 that it's essentially impossible to give a meaningful explanation of their overall ideology. "Like the Republicans, but maybe not quite as much" is disturbingly close to the truth. A party can only throw its support behind so many wars before they can no longer sell themselves as anti-war and so many neoliberal economic ideas before it can no longer claim to be usefully distinct from the right. The centrist Democratic Party has had some electoral successes; that is undeniable. It has also had some staggering failures, though, and its biggest shortcoming may be that it has left Democrats poorly positioned to recover from those failures. Lacking any real identity, the path to success, as was the case in the early George W. Bush era, seems to be to wait until people tire sufficiently of the Republicans and then elect some Democrats because our system offers no other real options.