"I don't think he understands that the words of the president matter," Warner told CNN's Fareed Zakaria in an interview set to air Sunday. "They matter not only in America but in many ways the words of the president matter even more in terms of how the world views our country."

Warner's comments came as Trump faces criticism for a pair of tweets sent Thursday that crudely and personally attacked "Morning Joe" host Mika Brzezinski.

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In the tweets, Trump called Brzezinski "low I.Q. Crazy Mika" and alleged that she was "bleeding badly from a face-lift" when she and her co-host Joe Scarborough visited Trump's Mar-a-Lago club in December.

The tweets sparked an uproar among both Democratic and Republican lawmakers, some of whom cast the attack as an extension of the president's poor treatment of women.