Transcript for Mueller investigating Trump Tower meeting

That's enough to sink this effort, but GOP leaders seem determined to get Republicans on the record on this issue that defines them for the last seven years. Mary Bruce on the hill. Thank you. In the meantime, the other major development tonight. The special counsel investigating Russian meddling. Robert Mueller is diving into a meeting at trump tower, as we learned tonight of someone new with the Russian lawyer. Here's our chief investigative correspondent, Brian Ross. Reporter: A new revelation tonight about that meeting at trump tower. Don Jr. Welcoming the Russian lawyer after he was told she had dirt on Hillary Clinton direct from the Russian government. The president's son says he's been transparent. So as far as you know, as far as this incident is concerned, this is all of it? This is everything. This is everything. Reporter: But tonight, the ever changing story changes again. The meeting first described by don junior as including five people, then seven people, today had an eighth person added to its roster. There was the Russian lawyer. Who said she didn't know trump was the nominee. The russian-born American lobbyist accused of being former soviet counterintelligence officer, and now a russian-born businessman named Ike kaveladze, who gained notoriety, but was not charged in an investigation of Russian money laundering in the year 2000. At the time, he called it a witch hunt. Kaveladze now is an executive for the Russian billionaire, and friend of Vladimir Putin, who helped set up that trump tower meeting. Yet another person left out of don junior's supposed full disclosure. Did you ever meet with any other persons from Russia that you know? No, I don't even know I've probably met with other people from Russia. I mean during the campaign. Certainly not in the context of a formalize meeting or anything like that because why would I? Brian Ross with with us now, and people will be saying, why are we hearing about yet another name that was inside that meeting? David, it really has been a slow drip, and it helps explain why this meeting has become such a focus of the special counsel, Robert Mueller. His team wants to talk with each of the eight people in the room, and tonight, we have also learned from senator Dianne feinste Feinstein, that Mueller has given congress the okay to question don junior and former chairman Paul manafort in front of the American people, and both will cooperate.

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