Hillary Clinton has slammed Republican rival Donald Trump for making disparaging comments about women's physical appearance, accusing Trump of taking the issue of female body image "to a new level of difficulty and meanness".
Hours before US vice-presidential candidates Tim Kaine and Mike Pence were to face off in their sole debate, Clinton on Tuesday urged women at an event in Philadelphia to stand up to online bullying about how they looked.
"It's shocking when women are called names and judged solely on the basis of physical attributes," the Democratic presidential nominee said in response to a 15-year-old girl's question about body image.
"My opponent insulted Miss Universe," Clinton said, resurrecting Trump's comments last week about former beauty queen Alicia Machado's weight gain after she won the Miss Universe contest in 1996.
"I mean, how do you get more acclaimed than that? But it wasn't good enough," Clinton said.
"We can't take any of this seriously any more. We need to laugh at it. We need to refute it."
Clinton has rushed to capitalise on Trump's public feud with Machado, who he once called "Miss Piggy" because of her weight gain, and make inroads with women voters five weeks before the November 8 election.
Clinton's and Trump's running mates, Democrat Tim Kaine, a US senator, and Republican Mike Pence, governor of Indiana, will meet in a debate in Farmville, Virginia (Wednesday morning AEDT).
Pence could find himself on the defensive about Trump, who has been dealing with a torrent of bad news in the past week.
That includes a New York Times report that Trump took an almost $US1 billion loss in 1995 that might have allowed him to avoid paying federal income taxes for up to 18 years.
While Democrats have slammed him over the report, Trump has said he "brilliantly used" US tax rules to his advantage to limit his tax bills.
Clinton disagreed, telling reporters it showed "unequivocally" that Trump was a failure at business for losing $US1 billion to begin with.
Clinton also criticised Trump for appearing to suggest that veterans suffering from post-traumatic stress were not strong enough to handle the stress of war.
Trump and his campaign said his words were taken out of context.
"When people come back from war and combat, and they see things that maybe a lot of folks in this room have seen many times over - and you're strong and you can handle it - but a lot of people can't handle it," Trump told a veterans group on Monday.
Clinton said troops deserved a commander in chief who understood their sacrifice.
Meanwhile, Trump has revelled in comments on Monday by Clinton's husband, former president Bill Clinton, who said small-business people and people who make too much to get federal subsidies to help with insurance payments were "getting killed" by the healthcare law known as Obamacare.
Trump has promised to repeal Obamacare, while Hillary Clinton has praised it but said she would work to improve aspects of it.
