Republican presidential candidate Donald Trump has branded Hillary Clinton "disgusting" for apparently using the toilet during a commercial break at the last Democratic debate.
And he used crude language to describe her primary loss to now-President Barack Obama in 2008.
"She was favoured to win and she got schlonged, she lost," he said on Monday night, using a slang word for male genitalia.
Mr Trump, who has ramped up his criticism of Mrs Clinton in recent weeks, also mocked the Democratic front-runner for returning late to Saturday's debate following a commercial break because she'd been using the bathroom.
"What happened to her? I'm watching the debate, and she disappeared. Where did she go?!" he said at a rally in Michigan.
"I know where she went. It's disgusting, I don't want to talk about it," he added. "No, it's too disgusting. Don't say it, it's disgusting."
Mr Trump continues to the lead the crowded field of candidates vying for the Republican nomination in primary contests that start in just over six weeks. The development has alarmed many Republican Party leaders who fear the billionaire's incendiary rhetoric would make him unelectable in a general election face-off with Mrs Clinton, who is widely favoured over two rivals for the Democratic nomination.
This isn't the first time Mr Trump has used what could be interpreted as gendered language to criticise Mrs Clinton. He has repeatedly described her as lacking the strength and stamina to be president and invoked the image of her putting on a trouser suit before heading to work.
But the latest remarks appear to have hit a new nerve. After declining to comment on Monday evening, Clinton spokeswoman Jennifer Palmieri took to Twitter to label the language "degrading".
"We are not responding to Trump, but everyone who understands the humiliation this degrading language inflicts on all women should," Ms Palmieri said on Twitter, concluding with the hashtag "imwithher."
The latest rift between Mrs Clinton and Mr Trump began during Saturday evening's debate. She claimed the Islamic State group had used videos of his comments about Muslims to recruit militants.
"They are going to people showing videos of Donald Trump insulting Islam and Muslims in order to recruit more radical jihadists," she said.
There was no evidence to back the claim, and Mr Trump quickly called Mrs Clinton a liar and demanded an apology.
"She's a liar!" he repeated at the rally, labeling Mrs Clinton "not a president".
Mrs Clinton appeared on Tuesday in Keota, Iowa, a small rural town where three high school students launched an energetic campaign to get her to visit their school.
She did not refer to Mr Trump's latest comments on her 2008 presidential bid, but she made a veiled reference to his campaign when a student asked her about combating bullying.
Advocating for more "love and kindness" Mrs Clinton added: "That's why it's important to stand up to bullies wherever we are and why we shouldn't let anybody bully his way into the presidency. Because that is not who we are as Americans."