Transcript for Rep. Schiff: Cohen revelations 'deeply compromising' for Trump and our country

Good morning, we're coming on the air with major breaking news in the Russian investigation. Michael Cohen, president trump's former attorney, long-time fixer, has reached a new plea deal with special counsel Robert Mueller. He's appearing in federal court in Manhattan at any moment. Expected to plead guilty to false statements to congress. Centered on the key issues of collusion with Russia. That was the scene on Thursday morning. The latest move by special counsel Robert Mueller. Want to talk about it with congressman Adam Schiff. Congressman, thank you for joining us. I want to get to the implications of the Cohen plea deal. But first, your response to Roger stone there. He's denying any contact with wikileaks. Denies any contact with the trump campaign over wikileaks. Did you find his answers credible? No, I didn't. Not at all. And, in fact, the e-mails you read to him, those exchanges with Corsi, which I think he provided to the press, the substance of those e-mails are inconsistent with his testimony before our committee. The mere existence of those e-mails are inconsistent with his testimony before our committee. But nonetheless, his testimony was delivered with the same conviction that he made the statements to you this morning. That testimony really needs to be provided to the special counsel for consideration on whether perjury charges are warranted. You're saying based on what he told your committee that setting aside the underlying question of whether or not he was a conduit between wikileaks and the trump campaign, you believe he's vulnerable to charges of lying to congress? I do. What's more, the allegations in the criminal investigation, the draft information that Mr. Corsi was considering pleading to. If the substance of the allegations and Mr. Corsi has denied trying to mislead the special counsel. He hasn't denied the conversations with Roger stone. If that's correct, it looks like Mr. Stone was attempting to enlist Mr. Corsi's help with false testimony. It was Michael Cohen who pled guilty this week to false statements to congress. The admission he lied about working on the trump tower in Moscow to protect president trump. What does that tell you, the agreement and what you have learned about it tell you about Mueller's core areas of focus? It tells me a couple of things. It tells me he wanted to lock in Michael Cohen. There was no reason for that plea for the additional count. It's not going to materially affect his sentence. It has the benefit of making sure nothing changes down the road. That there's no pardon that causes this witness to go south. I think the likelihood of that was remote. But nonetheless, you don't like to take chances as a prosecutor. It also tells me that he wanted to put it all on the record. He wanted it in the public domain. That raises a concern for me. Why does Bob Mueller find it necessary to do that? Is it that he fears Mr. Whitaker will shut him down or prevent him from telling the country what happened? I think that is the procedural significance. The very broad significance here, George, is that there is now testimony. There is now a witness who confirms that in the same way Michael Flynn was compromised that the president and his business are compromised. And that is, the national security, former national security adviser Michael Flynn was compromised because he was saying things publicly that were not true about discussions with the Russians over sanctions. Now we have Michael Cohen saying that what the president was saying, what Michael Cohen was saying, and others were saying about when this business deal ended was not true. And what's more, the Russians knew it wasn't true. That at the same time that Donald Trump was the presumptive nominee of the GOP, and arguing in favor of doing away with sanctions, he was working on a deal that would require doing away with sanctions for him to make money in Russia. That is a real problem. That means that the compromise is far broader than we thought. You saw what the president had to say. First of all, he thinks Michael Cohen is lying. Then he had a backup argument. As well. Basically saying there would be nothing wrong if I were pursuing this tower. Here's what he said on Thursday. I was running my business while I was campaigning. There was a good chance that I wouldn't have won. In which case I would have gone back into the business. Why should I lose lots of opportunities? As he put in a tweet. This was very legal and very cool. Your response? Well, whether it was legal or not remains to be seen. It certainly wasn't very cool. More than that, it was very compromising of our country. In order for this trump tower deal to go through, sanctions had to be lifted on a Russian state bank. At the same time Donald Trump is out there pushing to lift sanctions on Russia and this bank. There is no way to describe that as cool or ethical or in the national interests. It means that the president, whether he won or lost, was hoping to make money from Russia. Was seeking at the same time to enlist the support of the Kremlin to make that money. And what's more, when this came to light, the Kremlin intervened. Mr. Peskov, the spokesman for the Kremlin, intervened, to help Donald Trump and his business in the coverup. That is so deeply compromising. And we have to remember what the Mueller investigation began as the Comey investigation was a counterintelligence investigation. An investigation into whether Donald Trump and his organization were compromised. And now via Michael Cohen, we find out that, yes, there was compromise. That puts our country at risk. Based on what we have learned so far, do you think others in trump's orbit have lied to congress about this as well? For example, don Jr.? We're going through the transcripts of the testimony. All of these need to be provided to Bob Mueller so he can make decisions. Bob Mueller has the advantage of far more information than we do that would allow him to vet whether what these witnesses told our committee was true or not. It's a pretty high bar to prove perjury. You have to prove there was a knowing intent to deceive. You have to prove there was not some failure of recollection. There are certain people I'm confident have met and exceeded the bar. I'll leave those determinations to Bob Mueller. He determined Paul manafort lied to him as he was supposed to be cooperating. With the special counsel. We learned also that he was sticking with the joint defense agreement talking to president trump's attorneys while on stens ibly cooperating with prosecutors. What is the significance of that? It means he was double dealing. He was going through the pretense of cooperating. He was in an underhanded way supplying information to trump legal defense team. The president continues to dangle a pardon for Paul manafort. It only adds to the growing body of evidence that the president is engaged in obstructing justice. That is the ultimate significance here. I think as a practical matter, the special counsel will have to throw the book at Paul manafort. As well as Mr. Corsi. You can't have people essentially in discussions with you flaunt that process, deceive you, if you want to telegraph to other witnesses that you darn well better be true when you say you want to cooperate with us. Congressman Schiff. Thank you. Thank you.

This transcript has been automatically generated and may not be 100% accurate.