Washington (CNN) President Donald Trump's lawyer, Rudy Giuliani, substantially weakened his case against Michael Cohen by going back and forth as to whether Cohen could tell federal prosecutors the truth, said Jay Goldberg, President Donald Trump's friend and former lawyer.

Giuliani called Cohen, Trump's former personal lawyer, "honorable" and truthful on several occasions before an audio recording of a discussion between Cohen and Trump about buying rights to a Playboy model's story about an alleged affair Trump took part in became publicized.

After CNN aired the audio, Giuliani called Cohen a "pathological liar" and said he doesn't "see how he has any credibility."

"I expected something like this from Cohen," Giuliani told CNN's Chris Cuomo on Thursday. "He's been lying all week. He's been lying for years."

Goldberg, who served as Trump's divorce lawyer for the President's first two marriages, said Giuliani "immeasurably" damaged his case against Cohen by changing his tune.

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