Transcript for Trump calls former secretary of state 'dumb as a rock'

cooperating with Mueller in the end. The president tweeting, totally clears the president. Thank you. Jon Karl on the president, who has been taking aim at Mueller all day, knowing this was coming. Reporter: Bracing for the special counsel's court filings tonight, president trump launched a series of Twitter attacks on Robert Mueller, and he declared, we will be doing a major counter report to the Mueller report. This should never again be allowed to happen to a future president of the United States! Already 87 pages done, he tweeted. All this, as the increasingly embattled president took fire from the secretary of state he fired. Rex tillerson, offering up a harsh assessment of the president he served. He is a challenging individual. A man who is pretty undisciplined, doesn't like to read, doesn't read briefing reports, doesn't like to get into the details of a lot of things. Reporter: Tillerson saying he needed to remind the president to obey the law. We did not have a common value system. When the president would say, here's what I want to do, and here's how I want to do it, and I'd have to say to him, well, Mr. President, I understand what you want to do, but you can't do it that way. It violates the law. Reporter: After tillerson's words today, the president tweeted, tillerson didn't have the mental capacity needed. He was dumb as a rock. He was lazy as hell. Jon with us live tonight from the white house. President trump today announcing his nominee for attorney general, who would replace Jeff sessions. And could eventually oversee the Russia investigation. And more on the tweet from the president, saying it totally clears me, thank you. What does he mean by that? Reporter: Well, there's nothing in these filings, David, that clears the president. So, it's unclear why he's claiming that. Nothing in any of these filings says anything that would suggest totally clearing the president. Regarding his pick for attorney general, an experienced Washington hand, William Barr. He served as attorney general for the elder George Bush many years ago. Jon, thank you. And tonight, after turmoil all week on Wall Street, the do

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