Pundits say Trump and his backers are increasingly relying on rhetoric that academics and even some Republican strategists say has an undeniable edge focused on gender.
He has repeatedly called attention to Clinton's voice, saying listening to her gives him a headache. Last December, he mocked her wardrobe.
The billionaire mogul has also used stereotypes about women to demean Clinton, who stands to become the country's first female president if she wins in November.
Trump often says Clinton doesn't look like a typical president.
A recent survey by the Pew Research Center found Clinton with a 19-percentage-point lead over Trump among women.