Democrats need to explain how typical left ideas are actually moderate and will help conservative voters.
Single payer, universal health care is awesome. Everyone gets healthcare, companies no longer have to pay, people get the same healthcare whether they work 20 hours or 40 or if they just start their own new business, and the government can pay doctors and hospitals directly instead of being micro managed by health care providers. A charismatic, strong leader could EASILY sell that message to working Americans but instead we get clowns who try to pander to healthcare lobbies and can't explain a fucking thing to regular workers.
Reducing defense spending is awesome. We spend way too much money on stupid ass weapons, ISIS isn't going to launch nuclear subs at us. We spend more than the next 19 countries, combined. Much of our defense spending is on pork projects lobbied by state reps who want to send another $1b in useless spending to their state. Again, a charismatic leader could easily send the message of reducing defense spending, focusing on America, not giving a shit about the middle east or protecting Europe from Russia or putting our noses in places it doesn't belong. Spend that money on infrastructure. Which is another huge bullet point.
Its literally a lot of things Trump won the election with (but defense increase instead of cuts), but every democrat (except Sanders I guess) is too afraid to run on that message because they think Americans will reject the platform. They are too stupid to realize that an America-first, take care of our own people, literally Make America Great again message will ALWAYS resonate with voters.
Yes - identity politics, police brutality, trans rights, and immigration are talking points that will always lose. Not necessarily because people hate them, but it sets up an automatic dichotomy of "us vs them", and "us" always wins in the voting booth. Once you win, and get some wins under your belt with healthcare and infrastructure, it will be easy to get some immigration, drug laws, and police reform measures passed. But those are the medicines you apply after everyone gets their candy, you don't lead with the message of "we all suck, time to do the right thing".
I don't have much hope though that a strong democrat candidate will come around that tries to appeal to working middle class folks but instead again tries to cobble together a bizarre coalition of the edges.