The second Republican presidential debate -- set for Wednesday at the Ronald Reagan Presidential Library in California -- will test front-runner Donald Trump in a way the billionaire firebrand wasn't in the first act, experts say.
Trump propelled his campaign from sideshow to headliner after the first Republican debate in Cleveland a month ago. His opponents treaded lightly then, expecting Trump to implode on his own, but they now find themselves foundering in his wake, the experts said.
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"He totally changed the dynamic, and I think he caught the field flat-footed," said Lee Miringoff, director of the Marist College Institute for Public Opinion. "They thought he would be a summer romance, but he has the support of a lot of the core primary voters."
"The gloves may be off," said Professor Meena Bose, director of Hofstra University's Center for the Study of the American Presidency. "A temporary irritant or complication is now a serious factor to contend with."
"I may be changing tactics," warned New Jersey Gov. Chris Christie, also once expected to be the GOP's brash, combative front-runner. He told "The Tonight Show Starring Jimmy Fallon" that if Trump again gets most of the airtime, the audience will see Christie and say, " 'Oh, he's going nuclear now!' "
The CNN debate at the Reagan library in Simi Valley begins with the second tier of candidates at 6 p.m. Eastern Time followed by those polling the biggest numbers at 8 p.m.
No one will seal the party's nomination at the debate, but the experts agreed the field will likely be winnowed. The second debate, as opposed to the first "overhyped" debate, will also force the party to confront "who we are and what do we stand for?" said Professor Mitchell S. McKinney, director of the Political Communication Institute at the University of Missouri.
For example, McKinney said, the Republican Party this year had planned to veer away from immigration issues after they hurt GOP nominee Mitt Romney in 2012. But Trump has brought a hard-line stand against illegal immigration to the fore, he said. "The party faithful remember what happened four years ago. They see it as a death knell . . . they wanted a 'big tent' " to include Latinos and other groups.
"As we continue through the series, we continue to flesh out what the Republican Party stands for based on the front-runners," McKinney said.
He expects policy clashes, such as the exchange between Christie and Kentucky Rep. Rand Paul in the first debate over whether homeland security should override civil liberties.
More desperate for a win on Wednesday will be the onetime presumptive front-runner, former Florida Gov. Jeb Bush, who lost 6 percentage points in last week's NBC News-Marist Poll among critical Iowa and New Hampshire voters since the first debate. Wisconsin Gov. Scott Walker sank further: 14 points in Iowa and 8 points in New Hampshire.
Former Hewlett-Packard CEO Carly Fiorina, who was in the second tier of candidates in the first debate, picked up 4 percentage points in each state and earned a spot in Wednesday night's prime-time debate.
Bush, who was silent in the first debate when Trump attacked immigrants here illegally, struck back last week -- nearly a month after Trump disparaged Mexican immigrants. His wife, Columba Bush, is from Mexico.
"You're damn right I'm going to fight back," Bush told a veterans group last week.
Former New York Gov. George Pataki, one of the long shots, attacked Trump as unable to win a general election or run a government: "I will work to get Democrats to support our conservative policies," Pataki said.
But politically the strategy will be more complex than making a splash that will move the polls for a few days, Bose said.
"I don't know if a candidate can hope to stop a . . . [Trump] campaign, but instead they can try to point out the flaws or perhaps emphasize their own strengths, rather than going on the attack," she said.
Bose said the difficulty lies in Trump's popularity -- voters don't want to be told they are backing a lame horse -- and his success at portraying himself as an outsider candidate. Longtime politicians can't easily criticize Trump for not knowing Washington if being outside Washington is his selling point.
"Usually we do see some attacks of the front-runner," McKinney said, "but this is a different front-runner . . . he's bombastic and returns fire in kind. And I think some candidates are afraid of that."
And overt attacks have backfired before. In July's debate, for example, Texas Gov. Rick Perry, who has since suspended his campaign, and Paul clashed with Trump briefly but failed to capitalize in the polls. "It shows it doesn't come easy, and it doesn't always work," Miringoff said.
Bose said a more surgical cut would be through a well-rehearsed quip delivered as cleverly spontaneous. "What they are hoping for is a good one-liner," she said.