She nailed it? You mean like how for 8 years she thought the border wall is a stupid idea and then suddenly she pivots into "yup, we totally need that wall"? Or when she got all buddy buddy with the likes of Cheney when the core democrats loathe Cheney? She had time to appeal to the republican voters but not to the 16 million voters who voted for Biden and not her? She had plenty of time to nail her campaign and she didn't.
And I'll just add this as a non-American. It's a very American thing to think election campaigns have to be long, because they are long in America. She got over 3 months to campaign and that would've been enough time in most countries. Just to give some context: Mexico's president campaigned for 93 days, Canada's last federal election was 36 days, Australian president campaigned for 36 days, India campaign was 33 days, Brazil was 90 days.
You are right about stupid people falling for stupid shit, but that's not why democrats lost. Trump got less votes than he did in 2020, that 70 million who voted for Trump are just people who love what Trump says.
What made democrats lose are the 16 million votes Biden got that Harris didn't get. The GOP didn't magically make those votes disappear, those missing votes is the failure of the democratic party.