Trump: "This is something nobody else can do. I can get the drug prices down...1000% 600% 500% 1500%.
Numbers that are not even thought to be achievable."

MAGA cheers and then wonders why people call them stupid...

He's not stupid, and neither are his supporters.

Trump isn't using those figures literally, and no one would reasonably understand them to be taken literally. It's "World's Best Coffee" territory:

YouTube: Worlds Best Cup of Coffee (prazfighta)

Trump comes from the world of real estate development (for the most part). If you make a statement with a specific factual claim in that context, you have to deliver - and expose yourself to liability if you don't. But if you make a hyperbolic statement that any reasonable listener would understand to be puffery, then you can't be held to any specific claim.

So when Trump says he'll reduce drug prices by 500%, neither he nor any Trump-leaning listener will take that as a statement actually promising negative prices. It's just signaling that he can substantially reduce drug prices - the number isn't relevant (and was deliberately chosen to be hyperbole), it's the generic claim.

And when Trump's opponents label statements like this as "lies," or "stupid," or whatever, it just makes the opponents look like folks that don't get it. Like Buddy the Elf in the clip above. Everyone who is savvy understands when something is puffery and not intended to be taken literally. The humor in the Elf clip is that Buddy is naive and doesn't have the sophistication to understand the actual context of the statement. So when WaPo adds this to their running list of Trump's lies, it's going to make WaPo just that much more foolish in the eyes of anyone open to Trump-leaning.