Trump's latest Clinton attack leaves David Gergen flabbergasted: 'This was a slanderous speech'

White House veteran David Gergen accused Donald Trump of going beyond a political attack on Wednesday with a "slanderous speech" against presumptive Democratic nominee Hillary Clinton.

In a speech delivered in New York, Trump suggested that Hillary Clinton did not have the "temperament" to be president, and that she should be in prison instead.

Gergen acknowledged that Trump may have helped his standing with Republican voters, but added that many voters would simply not believe the attacks on Clinton.

"You can't ignore the truth of what he says or the lack of truth of what he says," Gergen explained. "I do think in the coming days we're going to hear and awful lot about a string of lies and exaggerations."

For example, the CNN contributor said that he was shocked that Trump would rely on Peter Schweizer's controversial bookClinton Cash.

"That book has been basically discredited," Gergen noted. "He has no evidence that shows money given by donors to the Clinton Foundation then resulted in actions by the State Department that favored those donors. And what Schweizer himself has said is, 'Well, I think there's a pattern here and we ought to investigate.' I'm sorry, at this level, you can't slander somebody."

"And this was a slanderous speech," he added.

Watch the video below from CNN, broadcast June 22, 2016.