Charles Krauthammer said on The Kelly File that Donald Trump was winning the final debate "on points" and then "blew it up" when he refused to commit to accepting the election results.
"This was political suicide," Krauthammer said, explaining that Trump's task tonight was to "stop the slide" and convince more voters that he is an "acceptable" alternative to a Hillary Clinton presidency.
Krauthammer said Americans want a "change agent," but don't want a "radical who will challenge the foundations of the republic."
"You don't challenge the legitimacy of an election. I think that was a terrible mistake," he explained.
Krauthammer noted that Trump was likely coached by his advisers on a better answer to give, yet still decided to take the stand that he did.
Otherwise, Krauthammer said Trump was "calm and contained" and could have walked away with a victory, but instead his comments on the election's legitimacy will be the dominant headline.
Krauthammer also applauded Fox News anchor Chris Wallace as the big winner of the debate, calling it "the best moderator performance I've ever seen."
He praised Wallace for keeping the candidates engaged in long, substantive discussions without interruptions.
Watch his full analysis above.