Transcript for Highly anticipated testimony from diplomat at center of Ukraine controversy
It is a big day. Let's get right to the latest on the impeachment showdown. What could be the most critical day so far about to begin on capitol hill. All eyes on ambassador Gordon sondland, the man in the middle of this controversy about to testify this morning. Cecilia, he had the most direct contact with president trump. President trump has called him a good man and a great American. Sondland admits to telling Ukraine they wouldn't receive military aid for a white house meeting unless they publicly announced political investigations. The big question this morning will he now say that he was following orders from the president? Our senior congressional correspondent Mary Bruce starts us off from the hearing room on capitol hill. Good morning, Mary. Reporter: Good morning, George. This could be the most explosive testimony yet. In just a short time Gordon sondland, the diplomat at the center of the Ukraine controversy will be sitting right here grilled about the role he played and the role that the president played in pushing Ukraine to investigate trump's rivals. Sondland is a trump megadonor who became his point person in Ukraine. He has had more direct conversations with the president than any other witness. Those conversations today will be under an intense microscope and sondland has already revised his testimony once. The question here today, will he change it again? This morning, the most anticipated witness yet. Gordon sondland, the trump megadonor turned U.S. Ambassador to the eu who became the middleman between president trump and the Ukrainians. Ambassador sondland was in discussion with Ukrainian counterparts with fellow diplomatic personnel and the president, as well as at least one U.S. Senator about the course of events that we are investigating. Reporter: Sondland has already revised his testimony to admit he personally told the Ukrainians they would not souvenirly $400 million in critical military aid unless they publicly announced the political investigations trump was demanding. The big question today, was he acting on direct orders from the president? Trump has tried to distance himself. Let me just tell you I hardly know the gentleman. Reporter: But other witnesses say sondland a. A wealthy hotel mogul bragged about his frequent contacts with the president. Diplomat David Holmes testified he overheard one of their phone calls in a restaurant in kiev. Holmes said sondland told him the president didn't give an expletive about Ukraine and only cared about big stuff like the Biden investigation. Mr. Sondland has to decide whether his primary loyalty is to America or whether his primary loyalty is to the president of the United States. Reporter: It comes after a whirlwind day of hearings. Kurt Volker and a key witness requested by the Republicans claimed he didn't realize the investigations trump was demanding were into the Bidens but admitted he should have. In retrospect I should have seen that connection differently an had I done so I would have raised my own objections. Reporter: For the first time the public heard from firsthand witnesses who were on the call that sparked this impeachment Frankly, I couldn't believe what I was hearing. Reporter: Lieutenant colonel Alexander vindman a decorated war veteran on the national security council called trump's actions improper and a partisan play and reported it to his superior. But Republicans questioned vindman's loyalty. Mr. Vindman, you testified in your deposition that you did not know the whistle-blower. Ranking member, it's lieutenant colonel Alexander vindman, please. Lieutenant colonel Alexander vindman, you testified that you did not know who the whistle-blower was or is. I do not know who the whistle-blower is. Reporter: At the white house the president attacking vindman in realtime. I don't know him. I don't know as he says lieutenant colonel, I understand somebody had the misfortune of calling him Mr. And he corrected I never saw the man. I understand now he wears his uniform when he goes in. Reporter: After nine hours of testimony, the democratic chairman Adam Schiff concluding with this stark message for Republicans. Their objection is that someone blew the whistle. That's their objection. Not that the president engaged in this conduct but that he got caught. Reporter: Now sondland's testimony is just the first one that we will hear today. After him two more officials will testify here. They are plowing through these hearings, George at a head-spinning pace. It is all about ambassador sondland. I was struck by this quote from one of his closest allies, mark meadow says the impeachment effort comes down to one guy, ambassador sondland, all the other testimony has a sondland core to it and a sondland connection. Reporter: They are expressing concern that sondland could go further today than he has in the their fear is that sondland is a wild card and that he could essentially flip on the president. Okay, Mary Bruce, thanks very much. Let's talk more about with chief legal analyst Dan Abrams. Mary talked about in her piece is that so many other witnesses have contradicteds things that ambassador sondland said in his deposition. Right, and they're all talking about I talked to sondland. Sondland told me. Sondland was basically expressing the view of the president and that's why he's so important. He is sort of the Michael Cohen of Ukraine. The kind of enforcer on behalf of the president and the question is, how directly is sondland going to say the president told me to do this, not Rudy Giuliani, not Pompeo, but the president? I talked to the president because any time you have someone in between the president and somebody else, the answer can always be, well, Rudy went rogue. We didn't know what Rudy was doing. So the question would be how closely does he tie the president to this and how closely does he tie Rudy to the president and one thing we heard from ambassador Taylor is this is not a one-off but had five conversations with the president. Absolutely and the most important thing he's going to say today is there was a quid pro quo. We know he's going to say that. He's going to say that a white house meeting at the very least was conditioned upon investigation into 2016, investigation into burisma and that's sort of what sondland's job was in this Ukraine business was to basically say, look, we can get this meeting. We can get you the white house meeting but you're going to have to do these other things. The question is, what will he say about the aid. It is much more problematic if the link was to the aid rather than just the white house meeting. Any question in your mind he's the most important witness Absolutely not. If you believe sondland and think he's important the president is in trouble. If you either don't believe sondland or don't think he's important then there is no real issue. Dan, I know you're sticking by and joining our coverage of the house impeachment hearse that begin at 9:00 eastern right here on ABC.
This transcript has been automatically generated and may not be 100% accurate.