The big overarching problem is that the Democrats are in beigeout and refuse to stand for anything half the time. They are less interesting than the Republicans by far, and everyone knows it. Just take the two big memes of the Republican primary race: On one side, you've got crazy Donald Trump who just drops the dogwhistle for nearly everything and calls Mexicans rapists then posts himself eating Taco Bell on Cinco de Mayo, and on the other you've got Jeb!, heir to the Bush dynasty.
Trump triumphed over these other assholes in the primary because they were all to a greater or lesser extent Jeb!like, they were boring and conventional. Old news. It's the perfect environment for Trump's recursive hype.
Bland neoliberal corporate stasis isn't just a bad idea (and frankly, that's still Trump's real policy agenda even if he rails against it rhetorically), it does not engage voters and never will.
There's this really good quote about the Nazi Party that I can't find, but it amounted to "Hitler promised the people a rejection of the unbearably reasonable slow recovery of German power in exchange for absolute hatred and self-destruction, and they loved him for it". That same principle is why people are so often inexplicably Republican-by-Default, even people who don't seem to believe in the policies of the Republican party. It's not about the policies. It has never been about the policies.
Human beings view the world through a lens of narrative and storytelling, we have no "rational mind" so much as we can carefully curate our abstract feelings towards a practical goal, and that's basically a learned skill. Trump is a heel, and he knows it. Motherfucker actually did wrestling even if he was bad at it. But here's the thing, Clinton wasn't a face. She was nobody to the crowd of undifferentiated voters who split the difference between absolute victory and absolute defeat.
If there's anything to learn from the social dynamics of the Trump presidency it is that people prefer a villain to a bureaucrat. You need someone who is able to go beyond cynical memorization of facts and flaws in your opponent. You really, honestly need someone able to step into the narrative role of heroism if you want to split that difference and get people who don't give a shit about learning your website's fact checking on your side.