Objectively I don't think Biden was a bad president, and no I didn't vote for Trump.
They also never took a principled stand on it. Biden and Harris never said "the trade policy of Reagan and Clinton was a mistake and we are reversing it." If Harris had said that, she would have flipped Michigan and Wisconsin and maybe Ohio. With one sentence. Throw in "the Iraq war was a mistake, and while I support Ukraine we need to make sure we don't repeat the mistakes of the past" and she might have flipped a few more.
If that's at all what Harris thinks, then the Democratic Party has an enormous communication problem. They don't know how to connect and they don't claim their wins. They sound like their whole communication agenda is set by consultants and PR people, because it is, and when people hear that they dismiss it as bullshit because everything consultants and PR people say is bullshit. That communication style is a huge contrarian indicator. When people hear a press release they tune out.
The right has learned how to talk to people. Or rather, they've un-learned the communication playbook of the latter half of the 20th century. That's why they're winning.
I knew Harris was going to lose when she skipped Rogan for SNL. I'm not a big Rogan fan (he's gone way downhill since his early years) but he's how you reach people today. Nobody cares about SNL.
I think a good first step would be to start listening to people like AOC -- not necessarily about all her policy views but about how she communicates. She communicates like a 21st century politician, not like someone from 1980.