Whether any one candidate "won" the first U.S. Republican presidential debate may not have been nearly as important as the overall performance of front-runner Donald Trump. 

And on that front, the billionaire businessman may have caused his campaign some damage.

"The real story is the collapse of Trump in this debate," conservative columnist Charles Krauthammer told Fox News' Megyn Kelly, one of the moderators of the debate.

"That was supposed to be his night, the expectations were particularly high ... I thought he had a flat night and one that I'm not sure he's going to like."

Florida Senator Marco Rubio certainly had a solid night, while former Arkansas governor Mike Huckabee, Texas Senator Ted Cruz, New Jersey Gov. Chris Christie and Ohio Gov. John Kasich were all strong performers. 

Two of the other top-tier candidates, former Florida governor Jeb Bush and Wisconsin Gov. Scott Walker made no mistakes, but seemed to play it safe, delivering somewhat underwhelming performances.

APTOPIX GOP 2016 Debate

Donald Trump earned the ire of the crowd, and likely many Republican supporters in general, when he would not commit to supporting the party's eventual nominee and would not rule out running as a third-party candidate. (John Minchillo/Associated Press)

In fact the night, in terms of winners, may have belonged to Carly Fiorina. The California businesswoman was the clear stand-out among pundits in the so-called 'kids-table' debate that took place hours before the prime-time contest for candidates with low polling numbers.

But the night was really all about Trump, and how he was able to handle himself. 

'Damaged him considerably'

He immediately earned the ire of the crowd, and likely many Republican supporters in general, when he would not commit to supporting the party's eventual nominee and would not rule out running as a third-party candidate. Many believe a third-party run would only split the Republican vote and ensure a Democratic victory.

"That, I think, damaged him considerably," said Republican strategist Ron Bonjean. "I think his numbers will slip because of that. It just didn't show loyalty to the Republican party."

Aaron Kall, director of debate at the University of Michigan, said that while Trump did eventually recover, it was a horrible start. 

'You couldn't imagine there being a scenario that started out worse for the front-runner.' - Aaron Kall, University of Michigan

"I think if you would have tuned into the first five minutes of the debate, you would have said he blew it. You couldn't imagine there being a scenario that started out worse for the front-runner," he said.

As for Trump's exchange with Fox News moderator Kelly over the issue of derogatory comments he's made against women, it's hard to say what impact that will have on his campaign.

Kelly recited a list of nasty insults Trump had hurled at women, terms that included "fat pigs, dogs, slobs and disgusting animals." Trump defended his actions, joking that those insults were directed at actress and comedian Rosie O'Donnell (the two had a tiff years back). But he also said many of those comments should not be taken so seriously and that people need to stop being so politically correct.

His conservative credentials were also tested. He was asked about his past support for Canada's one-payer health-care system, a policy strongly opposed by Republicans who have pledged to overturn Obamacare. Trump responded that the policy works for Canadians, and also works in Scotland, but that he favours privatized health care in the U.S.

He was also questioned about his past financial support for Democratic candidates, including then New York senator Hillary Clinton, and asked what he got back in return for that support. Trump shot back that he got Clinton to go to his wedding. 

"I thought Trump lost this debate because he's sitting on top the mountain and now people will have the chance to pull the curtains back and they can see he's not a reliable conservative," Bonjean said.

'Drop in the polls'

"I think he will probably drop in the polls now because he was forced to talk in more than soundbites. Some of the things he said were head scratching."

Part of the problem for Trump may have been the debate format itself, which reined in the free-wheeling candidate.

"​Here's what killed him  — that tight controlled setting," said Republican strategist Ford O'Connell. "Trump is great if you let Trump go on his own. Trump has to figure out to make the same points he makes when he is basically unfiltered, in a tight controlled debate setting."

"When somebody can't control themselves up there and and continues to challenge questions, it doesn't leave you with the impression that you can sit in the Oval Office."