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David Letterman is no fan of Donald Trump.

In a preview of his interview with Tom Brokaw, which airs Sunday, the retired "Late Show" host had some strong words about the presumptive Republican presidential nominee.

"I understand that he’s repugnant to people," Letterman told Brokaw. "But you tell me, the men putting together the Constitution, witnessing this election, wouldn’t they have just said, 'Well, that’s part of the way we set it up. Good luck.'"

He explained that Trump won the nomination fair and square, and there's nothing illegal going on.

"He’s just despicable," Letterman said, adding that Trump may very well prove the saying that "anyone can grow up to be president."

This isn't the first time Letterman has gone after Trump. Last summer, he joined Steve Martin and Martin Short onstage in San Antonio to deliver the "Top 10 Interesting Facts About Donald Trump."

Watch the clip above and see Letterman's scathing "Top 10" on Trump below.

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