NEW YORK (AP) -- Donald Trump and his Republican allies say Hillary Clinton is weak, lacks stamina and doesn't look presidential.
Intent on undermining his Democratic rival, Trump and GOP backers are increasingly relying on rhetoric that academics and even some Republican strategists say has an undeniable edge focused on gender. Trump notably belittled his primary rivals, tagging Jeb Bush as "low-energy," and disparaging Ted Cruz as "Lyin' Ted," and Marco Rubio as "Little Marco." His criticism of Clinton goes beyond "Crooked Hillary," and complaints about her use of a private email server as secretary of state and her foreign policy decisions.
Clinton, Trump said in a speech last week, "lacks the mental and physical stamina to take on ISIS and all the many adversaries we face."
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 the country's first female president if she wins in November.
A frequent point of criticism: Clinton doesn't look like a typical president.
"Now you tell me she looks presidential, folks," he said at a recent rally in New Hampshire.
"I look presidential," he insisted.
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 her tenure 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."
"She is the first women from a major party running for president, so gender is always at play," said Dianne Bystrom, the director of the Carrie Chapman Catt Center for Women and Politics at Iowa State University.
Clinton pushed back Monday against the insinuations she's in poor health, saying on ABC's "Jimmy Kimmel Live" that "I do feel sometimes like this campaign has entered into an alternative universe. I have to step into the alternative reality and, you know, answer questions about, am I alive, how much longer will I be alive, and the like."
Gender has always been tricky for Clinton. Throughout her career, she has struggled with how to confront gender norms, ranging from the extent to which to embrace the historic potential of her candidacy to whether she should be referred to by her given or married name.
Trump, meanwhile, has sought to undermine that advantage, accusing Clinton of "using the woman card" to boost her appeal. The attacks have not helped: A recent survey by the Pew Research Center found Clinton with a 19-percentage-point lead over Trump among women. Trump, meanwhile, has a 12-percentage-point advantage with men.
Katie Packer, a Republican strategist who founded a political consulting firmed aimed at appealing to Republican women, said that Trump has a history of seizing on his rivals' perceived weaknesses. In Clinton's case, she said, that appears to include her sex.
"He clearly views women as sort of the weaker sex so I think he's going to look to exploit that with Hillary," said Packer, who also helped to run an anti-Trump super PAC during the primaries.
His rallies are filled with blatant misogyny. Supporters wear "Trump vs. Tramp" political buttons, and have even harsher slogans and signs.
At the same time, Trump has a long history of hiring female executives and last week became the first Republican in the party's history to appoint a woman, pollster Kellyanne Conway, to serve as his campaign manager.
Trump's campaign did not respond to requests for comment Monday, though in the past he has dismissed such charges as "nonsense."
Yet Conway herself has advocated using Clinton's sex against her in the past.
Speaking to The New York Times in April, when she was still backing a Trump rival, Conway said Trump's efforts to turn Clinton's gender against her could prove effective.
"By taking gender head-on, Trump refuses to cede women voters and so-called women's issues to Hillary just because she is a woman," she told the paper. "He is 'Swiftboating' her by throwing shade on what should be a strength." Her mention of "Swiftboating" was referring to widely debunked efforts in 2004 to challenge Democratic nominee John Kerry's war record.
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 primary season when Trump was competing against a field of largely men, he took on the role of strong man, demeaning his rivals with put-downs.
"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."
But there's little evidence such attacks are effective when it comes to winning over women, Bystrom said., adding that Trump's gender attacks on Clinton risk turning off older women, who have faced discrimination in the workplace.