He has repeatedly called attention to Clinton's voice, saying listening to her gives him a headache. Last December, he mocked her wardrobe. "She puts on her pantsuit in the morning," he told a Las Vegas audience. At rallies and in speeches, the billionaire mogul has also used stereotypes about women to demean Clinton, who stands to become America's first female president if she wins in November.

Trump's allies have piled on. Running mate Mike Pence often uses the word "broad-shouldered" to describe Trump's leadership and foreign policy style, a tacit swipe at Clinton. Former New York Mayor Rudy Giuliani argued that all of the miles Clinton logged during as secretary of state resulted in more harm than benefit.

"Maybe it would've been better if she had stayed home," said Giuliani, who more recently questioned Clinton's health, suggesting an internet search of the words "Hillary Clinton illness."

Kelly Dittmar, a scholar at the Rutgers University's Eagleton Institute of Politics' Center for American Women and Politics, who has been tracking the gender dynamics in the race, said that even during the primaries when Trump was competing mostly against men, he took on the role of strong man, demeaning rivals.

"His message has been: I'm the manliest candidate, I'm the strongest, I know how to protect women - which is a pretty paternalistic take on it - I'm going to destroy ISIS and be very tough, to the point where he's talking about the size of his own manhood," she said of the candidate. "If you're trying to prove you're the manliest, then you're trying to emasculate your opponent."