Longtime Trump ally Roger Stone suggested that special counsel Robert Mueller is wasting his time investigating and charging former Trump campaign chairman Paul Manafort, claiming he'll never plead guilty to the charges leveled against him. In a wide-ranging interview with CBS Miami, Stone called Manafort "feisty and combative" adding that he's "not going to roll over on this president."

"Why they keep loading up charges against him to pressure him makes no sense to me because there's nothing that he can tell them that will make Donald Trump vulnerable. There is no Russian collusion," said Stone.

Manafort has been charged with more than 30 counts of bank fraud, making false statements to investigators and other charges in two criminal cases as part of the special counsel's Russisa probe. he has pleaded not guilty to the charges.

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When pressed on whether or not he felt Mr. Trump should sit down for an interview with Mueller himself, Stone said such a move was "completely unadvisable."

"At this point I don't think there's any evidence of Russian collusion or conspiracy or coordination. But I do think he could conceivably be vulnerable to some process crime, perjury, lying to an FBI agent, so on," Stone said.

CBS News' chief White House correspondent Major Garrett confirmed last week that Mr. Trump has already begun to informally prepare for a possible interview with Mueller. Such informal preparation is not unexpected — that Mr. Trump's personal attorneys have been negotiating over a possible interview with the special counsel for months has long been reported.

Sources close to the process say the range of discussion in terms of scope and manner are narrowing, and an agreement may come within one or two weeks, and possibly sooner.

As for Stone being willing to sit down with Mueller, the political consultant said he would be "willing to cooperate with an inquiry" generally speaking but said he is taking it as it comes.

Stone has since agreed to provide documents to the Senate Judiciary Committee originally requested by Sen. Dianne Feinstein, D-California, as part of the panel's own Russia probe. Feinstein requested a long list of documents, including any communications with WikiLeaks and its founder Julian Assange, Russian officials, and all Trump campaign officials.

Stone has repeatedly denied working with Russia to influence the campaign.