Trump told Zelensky he "would like him [Giuliani] to call you".
Klimkin listened in when former Ukrainian President Petro Poroshenko held phone calls with Trump, but said he had never heard Trump raise Biden in those conversations or try to extract a personal favour in return for USA military aid.
In Kiev, opponents have lashed out against the "disaster" call but supporters say the transcript released this week showed Zelensky playing Trump to his own advantage.
"Leshchenko told me and a colleague that officials around Ukraine's president Zelenskiy understood that talking about Biden was a condition for any meeting with Trump". That investigation had been dormant for more than a year, Ukrainian officials say, when the USA and its European allies pressured Ukraine to fire the prosecutor for being too lax on corruption cases.
Even before the whistleblower complaint was made available to lawmakers, House Speaker Nancy Pelosi on Tuesday declared Trump had betrayed his oath of office and announced she was opening a formal impeachment inquiry into the President. "I would like you to find out what happened with this whole situation in Ukraine, they say CrowdStrike ..."
A CNN spokesperson did not immediately respond to a request for comment. After Ukrainian President Volodymyr Zelenskiy thanks Trump for selling anti-tank missiles to Ukraine, Trump proceeds to ask his interlocutor a favor.
Pelosi to back Trump impeachment inquiry
The complaint reportedly centers on Trump and a promise he made during a phone call with a foreign leader. As Pelosi was speaking, Trump dismissed the move by Democrats as "witch hunt garbage".
The documents are part of an allegation against Trump that he pressured the Ukrainian president to investigate the son of former Vice President Joe Biden and his business dealings in Ukraine.
Giuliani also said he had a "nice little trail" of text message conversations with the top United States diplomat to Ukraine, Kurt Volker, to prove his story.
"And the witch hunt continues, but they're getting hit hard on this witch hunt, because when they look at the information, it's a joke", Trump claimed.
The New York Times' Kenneth Vogel made this point-and it pretty much exposes the whole Trump-Ukraine circus as a nothing burger, just like the collusion nonsense.
Zelenskiy told reporters on Thursday that he doesn't know the details. "He's gone rogue", she said, per Politico. Hakeem Jeffries, a Democratic congressman from NY, asked on Wednesday. "As discussed, connecting you here with Andrey Yermak, who is very close to President Zelensky". He said he was "grateful for any assistance to Ukraine from our European leaders, from Ms. Merkel, from Mr. Macron, and from others", he said.
Rudy Giuliani, President Donald Trump's personal attorney, said it should be "impossible" for the Ukraine whistleblower to be considered the "hero" when he is the one acting in the government's interests.