As a non-US, I see very little difference between democrats and republicans, except maybe Trump. Democrats are the typical neoliberals: free markets, global capitalism, corporate rule, worldwide patents, etc. There is the famous chart that shows that since around the 80s the productivity went up while wages stagnate. Workers in the US right now are not in a much better position than 20 years ago.
Did the democrats campaign for improvements, raising the wages, improving healthcare, education? No, it was business as usual, "please don't vote Trump so we can keep things like now". Thus, many people said "fine, I'll vote for the other, he says things will be like before, literally".
So it's the Democratic Party who has baked into its DNA that things should not change, no matter what. I would say they could've won easily with some concessions, but those concessions go against their core beliefs.
Unfortunately, and because of this, Trump, a liar and conman, won. If they wanted to win they should've lied better, like Trump did.