What if he wins the popular vote? Will that impact the zeitgeist?
Yep. There would be questions as to what the purpose of the left is and what it can do. Harris' shortcomings would be blamed by some, sexism by others, debates from various perspectives. If the Dems lose the PV it'd really cause a deep crisis of confidence and calls for various adaptations would follow.
As I see it, post-Reagan, the left has struggled with its identity. The basic concept pre-Reagan was to use government to make peoples lives better. The disputes were about the how to do that, but not if it should do that. Nixon founded the EPA, because both sides basically accepted that central premise of the role of the state. Post-Reagan, the perception that government is the problem was accepted near 100% by the right, and even some longtime Dem voters have accepted it, which is really limiting. The government is unable to really get muscular and flex its might if it accepts that basic premise.
The tendency of Dems to pivot to the center so as to be more palatable to the overall majority is pretty reflective of that. When in doubt, rather than win people to their preferences, they scale them down to capture the perceived majority.
I think people support Dems today for 3 primary reasons, each about 33%. Roughly.
Group A want the state to go hard to make peoples lives better
Group B want limited state flexion ultimately, but not zero
Group C believe the role of the state should be to promote equality between various identity groups(usually most concerned with theirs)
I'm personally in group A. If they lose the PV they'll see great friction between all 3 groups as it seems their goals do not necessarily align. To pursue any of these approaches fully has opportunity costs. Can't really commit to any without displeasure and this results in the perception nothing gets done by groups A and C, with only B content because they're pretty limited to begin with.
But then, if you want B, Republicans increasingly are your party. Preference for limited change in a rapidly changing world really needs the state to artificially maintain it, and R's are increasingly moving towards that position and away from a do-nothing preference for the state. Emotionally, not much gap there to begin with. Limit change.
I think it'd be best if group A won in the internal dem debate after but I doubt that'd happen. Future Dem leaders would give B even more primacy because they're most relevant in swing states, which Kamala is actively doing now. A would be sidelined. C hasn't gotten much buy-in on the ground to begin with and would probably be most harshly criticized.
Interesting thought exploration, though