WHITE HOUSE -- There's a high-power, high-profile addition to President Trump's personal legal team: Rudy Giuliani, whose resume includes U.S. attorney for the Southern District of New York. The hiring of Giuliani comes as allies of the president are concerned another of his personal lawyers, Michael Cohen, could flip.

The former New York City mayor and longtime Trump supporter says he is joining the president's legal team to help end the Russia investigation. In an interview with The Washington Post, Giuliani said, "I hope we can negotiate an end to this for the good of the country."

As recently as Wednesday, the president again denounced special counsel Robert Mueller's work.

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Cohen sparks concern

"This is a hoax," Mr. Trump said. "We are hopefully coming to the end. It is a bad thing for our country -- very, very bad thing for our country. But there has been no collusion."

The president downplayed the likelihood he would fire Mueller or deputy Attorney General Rod Rosenstein, who oversees the investigaton.

"They've been saying I'm going to get rid of them for the last three months, four months, five months," Mr. Trump said. "And they're still here."

Mr. Trump has also tried to undermine the investigation by attacking former FBI officials. He has zeroed in on the conduct of former deputy FBI director Andrew McCabe, who has been accused of being deceptive about his contacts with the media.

Cohen investigation fallout

The Justice Department's Inspector General has asked to the U.S. attorney's office in D.C. to consider charging McCabe with a crime.

A lawyer for McCabe called the criminal referral "unjusitified," but former FBI director James Comey told CNN that if his former deputy is prosecuted, he could testify.

"I think it is accountability mechanism working and they should work because it's not acceptable in the FBI or the Justice Department for people to lack candor. It's something we take very seriously," Comey said on CNN.

The Justice Department said THurday it would turn over to Congress the memos that Comey says he wrote about his conversations with the president. In the department of transparency, CBS News sources say they are more detailed than Comey has represented in public and the White House legal team believes they are more favorable to the president than how the president has been represented in his new book.