Transcript for Trump battling democrats on their impeachment investigation
and president trump battling Democrats on their impeachment investigation and we're learning what the U.S. Ambassador to the European union plans to tell congress as it looks into whether Ukraine was asked to investigate Joe Biden and his son. ABC's David Wright is at the white house this morning. David? Good morning, whit. Reporter: The U.S. Ambassador is prepared to testify that the text message from president trump was relayed to him by the president. Meanwhile president trump continues to push back hard. President trump says he has nothing to fear from the Democrats. Impeachment? I never thought I would see or hear that word with regard to me. Reporter: "The Washington post" reports that trump's former ambassador to the eu plans to testify this week he did not write a text message that seemed to exonerate trump. In a September 9th exchange central to the impeachment inquiry the top U.S. Diplomat in Ukraine appeared to question the administration's effort to convince Ukraine's president to investigate trump's political rival, Joe Biden, allegedly by withholding $400 million in U.S. Military aid for leverage. The diplomat Williams Taylor texted I think it's crazy to withhold security assistance for help with a political campaign. Four hours later the U.S. Ambassador to the eu Gordon sondland texted back the president has been crystal clear no quid pro quos of any kind. Sondland then suggested to take the conversation off line. The president continues to insist there was no quid pro quo. The whistle-blower said quid pro quo eight times. It was a little off. No times. Reporter: According to the "Washington post" sondland is prepared to tell congress he has no idea if that's true, but the language was relayed directly to him in a phone call with trump himself. Sondland is also reportedly ready to tell congress that for months he worked at the direction of Rudy Giuliani. The president defended Giuliani. He's a man that looks for corruption. I know he's an honorable man. Reporter: Although Giuliani appears to be in the cross hairs of the investigation president trump continues to signal his support. According to "The New York Times" the two had lunch at the president's golf club in Virginia. The president tweeted his praise calling Giuliani the greatest mayor in the history of New York City. Dan? Standing by Giuliani thus far. David Wright at the white house. Thank you very much. A lot to talk about here. Let's bring in ABC's Jonathan Karl our chief white house correspondent who will be anchoring "This week" later. Jon, good morning. Let's start with this reported testimony upcoming from ambassador sondland. It could be problematic for the president, it doesn't actually prove there was a quid pro quo. Doesn't prove the United States or the president withheld military aid unless the Ukrainians investigated Biden. How damaging is it really? Reporter: First of all, ambassador sondland's words in those text messages you heard David talking about have been citing over and over again by Republicans. Sondland said in the text message the president has been perfectly clear there was no quid pro quo. Now this report from the "Washington post," if he's going to say that was what the president told him, but he doesn't know if it's true, it hurts one key Republican talking point. The bigger picture here is he's a witness coming to testify, the second witness in a week that's come to talk to congressional investigators in defiance of the white house, in defiance of the administration which has said they don't want anybody testifying. That is a big no question about it. Let me switch gears and turn to the democratic race for president which of course is overshadowed by the impeachment inquiry. We're two days away from the next debate. You got a chance to sit down with senator Bernie Sanders of Vermont who recently had a heart attack. Let's listen to your interview. Let me ask you, you and Elizabeth Warren have similar opinions on big issues. Not quite. What do you say to people that would pick her because she's eight years younger than you and didn't have a heart attack? Look, on the positions you're pretty much the same. Every American has to make his or her own choice. About the candidate they want. Elizabeth Warren has been a friend of mine for some 25 years. I think she's a very, very good senator. There are differences between Elizabeth and myself. Elizabeth has said she's a capitalist through her bones. I'm not. I am I believe the only candidate that's going to say to the ruling class of this country, the corporate elite, elite enough with your greed and corruption. We need real change in this Bernie gingerly differentiating himself from Warren. I guess the real question is how damaging is this heart attack to his candidacy? Reporter: Well, the question I asked him is a question a lot of voters are asking. Dan, he looked amazingly great. I went in the backyard with him and played some baseball. There he is getting a couple hits off me. He's going to be out on the trail. We'll see how he looks in the debate on Tuesday. Clearly health will be an issue for him. He's going to have to show that he can still pull it off. I was surprised for a guy that just had a heart attack looking as good as he did. Indeed and your under hand pitching game is tight. Reporter: It's good. Thanks, Jon. Jon has a lot more coming up on "This week." He'll have his complete interview with senator Bernie Sanders. Plus he'll go one on one with treasury secretary Steve mnuchin on the administration's response to the Turkish military action in Syria, a big story. Which happens to be our next story on "Gma."
This transcript has been automatically generated and may not be 100% accurate.