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LAS VEGAS — Hillary Rodham Clinton went to Donald Trump's doorstep Monday to mock the Republican presidential front-runner on the eve of the first Democratic presidential debate.

The appearance at a boisterous rally of the politically potent Culinary Workers Union was a win-win for Clinton, letting her signal her support for an influential union while taking aim at the Democratic party's favorite foil. The union, which represents casino and resort workers, is trying to organize hotel employees and invited all of the five candidates in town for the debate to the rally.

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Clinton was the only one who showed up, clad in a red pantsuit that matched the crimson union shirts. She urged the workers to "say 'No' to Donald Trump."

Hillary Clinton spoke at the Monday rally in Las Vegas. John Locher / AP

"Some people say Donald Trump is entertaining," Clinton said. "I don't think it's entertaining when someone insults immigrants, when someone insults women."

The union has been trying to organize the Trump hotel for more than a year, before the billionaire leapt to the front of the Republican field with tirades against illegal immigrants. The union says it was approached by some of the 500 restaurant workers and maids at the hotel who wanted representation.

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"Mr. Trump said, 'Make America great,'" Maria Jaramillo, a housekeeper who's worked at the hotel for six years, said at the rally. "The Trump workers say, 'Start it here!'"

Eric Trump, an executive vice president at the Trump organization and the presidential candidate's son, said workers at the hotel are largely happy.

"For years the union in Las Vegas has been trying to unionize this hotel, and they have been incredibly unsuccessful," Trump said. "We have an incredible group of employees who have categorically rejected unionization."