To the best of my knowledge, Trump never called Barack Obama — the first black presidential nominee of a major party — stupid. Nor, as far as I know, did he ever during the bitter campaign of 2016 use that word to describe Hillary Clinton — the first female presidential nominee of a major party. By contrast, as the Post acknowledges, Trump has described Joe Biden as mentally deficient.

Clearly, then, Trump’s attack on Harris’ intelligence is not based on her race or gender. It’s based on the fact that (1) Trump is nasty as hell and (2) the attack has enough resonance to be effective.

Resonance/effectiveness is the key here. Trump could not have made criticism of Obama’s and Clinton’s intelligence stick, so he didn’t try. He could make criticism of Biden’s mental capacity stick, so he indulged in it.

Similarly, he thinks calling Harris stupid will resonate. Thus, he does it.