Charles Krauthammer joined Bill O'Reilly after the second Fox Business Network-Wall Street Journal Republican debate to reveal who he thinks helped and hurt their campaigns.

"The guy with the most at stake was Jeb Bush. Unfortunately, he had another weak night," Krauthammer said. "I don't want to kick him around, but it was not what he needed to do."

He said that he also though John Kasich and Dr. Ben Carson had relatively poor showings.

As for the winners, Krauthammer said that Marco Rubio had "his usual stellar night."

"It's simply amazing. There is no subject on which he is not fluid and forceful and passionate," Krauthammer said. "As usual, I think he led the field."

Krauthammer said that he thought Carly Fiorina and Rand Paul also did very well.

He acknowledged that Paul takes many unpopular positions, such as his opposition to increased military spending, but he presented his non-mainstream policies in a compelling way.

Krauthammer said that Ted Cruz also had a pretty good night, while Donald Trump apparently decided to hang back and "tread water," since he's leading in most polls.

Watch more above.

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