It wasn’t the one issue, it was just the one that stuck with people who needed an excuse to not show up and vote for a woman.

To add to what the other person said, the biggest enemy of the boring party that wants to make the country better and isn’t making up ridiculous claims is apathy. (Not truly just apathy, but also people have lives to lead and it’s not like they get the day off, and voting isn’t the center of their life)

Mostly just look at the polling numbers after Harris was announced and how they have slowly fallen since then. There may be other reasons of course, but I find it hard to believe that people who supported Harris ever have any less support for her on a topic when comparing her to Trump.