This doesn't seem based in reality. You don't go from majority support for you running to less than that and blame the other side. There are demonstrable actions and events that have a distinct link to her downward popularity.
When examining why someone lost you generally don't insinuate that the loser did everything right and the other side are just bad people and that's why they won. That's a recipe for learning nothing and repeating the same mistake over and over again. Which unfortunately seems to be the national policy position.
The biggest problem with her campaign was the one thing it was impossible to fix - the amount of time. Everything else is nitpicking and wish-casting.
And that's on Biden and his team, mostly. I do give credit to the party for actually forcing him out. That's a hard thing to do, and it's exactly what R's ought to have done to Trump a long time ago.