Seems to me that having Harris run was a big change. A huge one. Not to mention, she was significantly younger.
I don’t think there was anything the Democrats could have done this time. People worldwide decided to replace whoever was in charge with someone different, and the US was part of that. It was stupid but people are stupid and make stupid decisions when they’re upset. And people are upset about inflation even if their country’s leaders can’t actually do anything real to fix it, they gotta blame somebody.
So now we have to suffer for at least a little while. Hopefully sanity returns at some point.