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Charles Krauthammer says that no one should be surprised that Donald Trump is "completely undisciplined."

On "Special Report" tonight, Krauthammer said that the Republican nominee has been "shackled" and "handcuffed" over the past month by his campaign staff and made to read off teleprompters.

"But the minute you let him loose - meaning on the debate stage, where there is no prompter - and then immediately after when he's reacting, what emerges is his central weakness: vanity," Krauthammer said. "We have seen this all along."

He explained that Trump trusts himself and speaks his mind, whether he's continuing his feud with former Miss Universe Alicia Machado or bragging about not paying taxes.

"This is a man who, when he's personally attacked, has to reflexively respond to defend his self-image. That's what drives him."

Get more insight from the "Special Report" panel above.

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