I guess I mostly don't understand how anyone believed it.
He ran on lowering grocery prices, and he was going to do this by making tariffs. So his plan boiled down to "I'm going to lower prices by raising prices".
With Trump it can be tough to tell if it's idiocy of malice but at some point I suppose it's a distinction without much of a difference.
I've had multiple HNers message me saying that their gas bills and grocery prices have never been lower, and that since day 1 of the new administration prices have dropped. Looking at trends across all states, I wonder how they came to that conclusion at all.