SIMI VALLEY, CALIF. -- Former CEO Carly Fiorina Wednesday night took on Republican front-runner Donald Trump with some help from other candidates for president who had been foundering in Trump's wake but found their voice on the debate stage.

The 500 guests at the Reagan Presidential Library often cheered and applauded wildly, but this time, it wasn't for Trump.

In August, a Cleveland arena created a cheering section for Trump. Wednesday night, the smaller audience of guests selected by the Republican National Committee and the library more often cheered policy details that skewered an opponent. Often, that opponent was Trump.

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For three-plus hours, the candidates spoke forcefully on a wide range of issues from immigration to taxes to the Iran nuclear deal to defunding Planned Parenthood. Several were quick to take on Trump, while Trump overall was more restrained.

Trump defended his criticism of Fiorina by saying a Yale Business School professor called her one of the worst CEOs he's ever seen when she ran Hewlett-Packard.

"The company continues to be a disaster," Trump said. "It still hasn't recovered. . . . She can't run any of my companies, I can tell you."

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"You ran up mountains of debt" in Atlantic City casinos, Fiorina told Trump, "and you were forced to file for bankruptcy a record four times."

She said she helped the tech company survive the recession and stock market crash, and it has thrived, but such leadership creates enemies and critics.

"Leadership," she said, "is not about braggadocio. It is about challenging the status quo."

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New Jersey Gov. Chris Christie then interrupted them both and what he called their "childish back-and-forth." He said a jobless construction worker "could care less about your careers, they care about theirs. . . . Let's start talking about that on this stage . . . You are both successful people. Congratulations."

The candidates frequently focused on Democrats or Democratic frontrunner Hillary Rodham Clinton.

"There's not a place in the world where we're better off than we were six and a half years ago," said former Florida Gov. Jeb Bush.

He and others said the Obama administration and Clinton, his first secretary of state, failed to keep Russia, Iran and Islamic State terrorists in check.

Trump said Obama has been a poor negotiator, which has cost the U.S. security and respect in the world.

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"I would get along, I think, with [Russian President Vladimir] Putin and we would have a much more stable world," said Trump, playing up his business experience as a negotiator.

Turning to the Middle East, Sen. Ted Cruz said on his first day as president he would "rip to shreds" President Barack Obama's agreement with Iran. Cruz said there is no way to keep Iran from developing nuclear weapons under the deal.

"The single biggest national security threat . . . is a nuclear Iran," Cruz said.

Former Arkansas Gov. Mike Huckabee agreed it must be scrapped.

"This is a government that for 36 years has killed Americans, they kidnapped Americans, they maimed Americans," and "threatened the very essence of Western civilization," he said.

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Foreign policy was also a flashpoint between frontrunner Trump and once-favorite Bush.

Trump said Bush's brother, President George W. Bush, failed so badly in his final months in office that he prompted voters to make the mistake of electing Obama.

"Abraham Lincoln couldn't have been elected," Trump said.

Bush paused, then charged back: "He kept us safe," Bush said to cheers and applause.

"I don't feel too safe," Trump countered.

A lighter moment came when the candidates were asked what their Secret Service code names should be.

Bush said his should be "Eveready -- that's high-energy, Donald," alluding to Trump's derision of him as "low-energy."

"That's a good one," Trump said, giving Bush a low-five hand slap.

Trump joked his name should be "Humble."