Republican presidential candidate Donald Trump used a vulgarity to describe Hillary Clinton's loss to Barack Obama for the 2008 Democratic presidential nomination and then poked fun at her taking a bathroom break during a debate.

Trump's off-color comments about the Democratic front-runner at a campaign appearance on Monday night came a day after he called Clinton a liar for saying his proposal to ban entry of all foreign Muslims to the United States has aided Islamic State's propaganda efforts.

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"She was going to beat Obama," Trump said of Clinton in Grand Rapids, Michigan. "... She was going to beat - she was favored to win - and she got schlonged. She lost. She lost."

"Schlong" is a Yiddish slang term for a man's genitals.

Trump, who is leading the Republican field for the 2016 presidential nomination, also made a reference to Clinton returning to the stage late after a bathroom break during a Democratic debate on Saturday night.

"I thought she gave up," Trump said. "Where did she go? Where did Hillary go? They had to start the debate without her. Phase II. I know where she went. It's disgusting. I don't want to talk about it," Trump said.

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Trump's appearance was interrupted by hecklers who were ejected from the event. The real estate tycoon suggested the protesters might be "drugged out" and chided another group for being "so weak" they would not resist security guards' directions to leave.

Trump's blunt style and comments about Hispanics, women, Muslims and his rivals for the nomination have set much of the tone for the Republican race. His comments about Clinton were not the first time he has veered into vulgarity during the campaign. After a prime-time televised debate in August, he posted Twitter messages criticizing Fox News moderator Megyn Kelly and then made comments in a television interview that were widely interpreted as referring to her menstrual cycle. He denied that was his intention.