I can't believe the message some Dems get from this race is to swing even more to the left. If Biden wasn't the nominee, I'm not sure the Dems would've been able to recapture the Rust Belt. Just look at how other progressive Dems ran behind his numbers. I definitely don't see Harris playing well there if she's the nominee in four years.
Biden never really made a case for policy, so why should voters vote for Democrats downballot? The Democrats' message was: Trump is a uniquely bad person and we have to get him, and him personally, out. It sounds like voters heeded that message. They narrowly threw him out - but left the rest of the Party out in the cold.