Originally Posted by BassoonPlatoon

It is a mix of different things and it will be different for different demographics.
One thing that might have had more of an impact than people realize was the incident where someone seemed to say "Jesus is Lord" at a Kamala Harris event and got reprimanded. That I have seen people actually say turned them against her. So, one thing is that I think she underestimated religious voters, specifically Christians. I think it's mostly this.

Overconfidence. A lot of people were really talking her up and telling her how everything she was doing was huge and was very successful. Take the debate performance, there were a lot of people claiming that she obviously won. However, it's not judges that matter, did the voters think she won the debate?

Finally, for me personally, I think she did not expand her scope enough. From what I could tell, she made the campaign primarily about one or two issues.

I think these are top three reasons and, if I had been her campaign advisor, I would have been discussing these with her as they were happening.