Carly Fiorina and Sen. Marco Rubio (R-Fla.) stood out, Donald Trump had a bumpy ride, and Scott Walker and Mike Huckabee faded a bit into the background at the second Republican presidential candidates' debate, analysts said Thursday.

Eleven candidates slugged it out in a three-hour marathon that CNN, the host, said was watched by 22.9 million viewers. Four candidates who aren't polling as well -- including former New York Gov. George Pataki -- battled in a 90-minute prelude, for which Sen. Lindsey Graham (R-S.C.) appeared to win the most praise.

With so many candidates crowding the stage, "only a few" are ever able to break through, said Kevin Madden, communications director for Mitt Romney's 2012 presidential campaign. Madden is now with Hamilton Place Strategies in Washington.

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"Clearly, Fiorina and Rubio did themselves a lot of favors last night. Trump had an off night," Madden said.

Fiorina stood out for taking on Trump's derogatory remarks about her appearance and talking about drug addiction's toll on her family, Madden said, while Rubio scored well on foreign policy issues and appeared to be in command of his facts.

"He had incredible command on foreign policy," Madden said of Rubio.

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Trump, meanwhile, stumbled on foreign policy and seemed to give muddled answers when pressed for details, he said.

"The format favored substance. That's why Trump had a bad night, and Rubio and Fiorina stood out," Madden said.

Jeb Bush, the son and brother of former presidents, fared better than in the first GOP debate in Cleveland last month, analysts said. But the former Florida governor didn't do anything to leap out.

"His best three lines were about his mother, his wife and his brother -- not about himself," Marist College pollster Lee Miringoff said.

Further, Bush answered Trump's criticism about the tenure of former President George W. Bush by saying, "You know what? As it relates to my brother, there's one thing I know for sure: He kept us safe."

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It drew applause at the Ronald Reagan Presidential Library, site of the debate in Simi Valley, California, but might not play well in a general election, Miringoff said. "I'm not sure you'd want to run your campaign on 'My brother kept us safe,' " he said. "It's not a zinger for a national audience."

New Jersey Gov. Chris Christie had his best performance so far, said Larry Sabato, a University of Virginia political scientist and a longtime observer of presidential politics.

Christie played the populist card when he called Fiorina and Trump corporate CEOs who "could care less" about the career of a typical "55-year-old construction worker."

Sen. Ted Cruz (R-Texas) aimed for hard-core conservatives, and Ohio Gov. John Kasich "had New Hampshire in mind," Sabato said, by staking out moderate positions on immigration, health care and the notion of shutting down the government to defund Planned Parenthood.

Walker, Wisconsin's governor, and former Arkansas Gov. Huckabee didn't have much presence, experts said. After a second straight such performance, some Walker supporters are contemplating campaign team changes, The Washington Post reported.

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The debate wasn't as tightly regulated as the Cleveland debate and "we lost some folks," said University of Missouri political scientist Mitchell McKinney, referring to candidates.

McKinney noted that Graham scored well in the early debate by challenging some of his rivals, especially on their ideas. For instance, he badgered Rick Santorum into admitting an immigration bill the former Pennsylvania senator favored had gone nowhere.

But doing well -- or poorly -- in a debate isn't necessarily an indicator of how well a candidate's campaign is doing. It didn't work that way after the Cleveland debate.

"The last time experts tried to decide who 'won' a debate, many mistakenly thought that Donald Trump had struggled," University of Virginia political scientist Geoffrey Skelley wrote on the centerforpolitics.org site. "Maybe he had in their eyes, but Republican poll respondents thought otherwise. There's no question that the second Republican debate featured a large number of attacks on Trump. Whether or not they actually diminished him remains to be seen."