Conservative pundit Charles Krauthammer rated Donald Trump’s performance at the final presidential debate on Wednesday as good overall, but said the Republican nominee “blew it” when he declined to say whether he would accept the results of the November election.

“This was political suicide,” Krauthammer said.

The nationally syndicated columnist warned that the electorate does not 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 said.

Watch Krauthammer’s analysis:

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