Don't choose such a unpopular candidate as Kamala. Have a primary instead of appointing someone.
There are a plethora of reasons she's unpopular, she can's string two coherent sentences together without a teleprompter, she cackles at inappropriate times, she won't talk to anyone off the cuff, she doesn't give straight answers on policy questions thus the word salad meme, she fumbles critical questions like what would you do different in the last 3 years, what a terrible answer...
What I think I'm reading here is that you feel like Trump is a better public speaker than Harris.
Assuming that this is a genuinely held belief that you have, I suggest that you consider that perhaps this is very subjective.
the gaza issue also probably didnt win any points in pennsylvania etc
I have no love for Democrats but it's unclear to me that there's really anything they could have done. The common wisdom in the past had been that Trump is some kind of liability for Republicans, but at every turn he has been underestimated and I question that assumption.
To me Trump looks like a true master of his craft, and there is no line of carefully triangulated messaging that will resonate more with typical Americans than his stream of vitriol and lies.