I think it really just comes down to having the presidential nominee on tape saying
"grab them by the pussy"
The full conversation is horrific enough, but that one line "grab them by the pussy" has it all, its predatory, its fucking weird, its gross, pussy is a dirty dirty word, contempt for women, sexual pervert" etc etc
all distilled down into... pussy.
Donald Trump, on tape talking about pussy.
Its just too simple and direct to ignore. Give that to republicans who have been wanting to jump ship from the start and bam.