i wouldn't bring him anything that's unsubstantiated before i knew what it was actually about myself." last year, cohen testified before two congressional committees regarding russian election interference, but a source familiar with cohen's testimony tells cnn he did not testify that trump had any advanced knowledge of the trump tower meeting. now the president's attorney, rudy giuliani, is attacking cohen's credibility. >> the man is a liar, a proven liar. there's no way you're going to bring down the president of the united states on the testimony, uncorroborated, of a proven liar. i guarantee you, this guy is a proven liar. >> reporter: when just a few weeks ago, giuliani seemed to have plenty of faith in cohen's truthfulness. >> if he believes this is in his best interests to cooperate, god bless him. he should cooperate. i do not expect that michael cohen is go to lie. he's going to tell the truth as best he can, given his recollection, and if he does that, we're home-free. >> reporter: sources say cohen doesn't necessarily have