"First I've heard of it", he said, brushing off the question at the White House.

That company added to its board the son of then-Vice President Biden; Trump sought an investigation into the Biden family, and his defenders have sought to draw attention to that aspect of the story.

At a rally in Louisiana just hours before Yovanovitch's testimony, Trump spoke in rare personal terms about his own impeachment journey.

Taylor and Kent could not answer Rep. John Ratcliffe's (R-TX) question as to whether the July 25 call constituted an impeachable offense.

So Democrats are shifting to "bribery" to describe Trump's conduct, though it's not yet clear whether that charge will form the basis of an article of impeachment.

The top Republican on the panel, Rep. Devin Nunes of California, bemoaned the hearings as a "daylong TV spectacle".

Public impeachment hearings resume Friday with the testimony of former ambassador to Ukraine Marie Yovanovitch, who says she was ousted because the Trump administration believed she would not go along with plans to pressure Ukraine to investigate Democrat Joe Biden, a potential Trump White House rival in 2020. Trump also asked Zelenskiy to investigate a debunked conspiracy theory embraced by some Trump allies that Ukraine, not Russian Federation, interfered in the 2016 USA election.

Soviet-born Parnas is prepared to cooperate with the impeachment inquiry.

Pelosi compared Trump's actions with former President Richard Nixon's conduct in the Watergate corruption scandal that led him in 1974 to become the only U.S. president to resign.

Many Republicans want the identity of the whistleblower to be revealed to other lawmakers on the House Intelligence Committee.

The diplomatic community has rallied behind Yovanovitch in the weeks since the contents of Trump's call were disclosed, and some former diplomats have also called for the State Department and Pompeo to lend their public support to the career foreign service officer.

An estimated 13.8 million viewers across 10 broadcast and cable television networks watched the first day of proceedings, according to Nielsen ratings data.

They testified in defense of Yovanavitch amid what Kent called Giuliani's "smear" campaign against her; about the dangers of abandoning Ukraine as it faces Russian Federation; and of what Taylor called an "irregular channel" of foreign policy orchestrated by the president's lawyer and carried out by other Trump allies.

Republicans emphasized Yovanovitch's tangential involvement in the central narrative and repeated that Trump has broad powers to replace any ambassador - and many other officials - within the administration. The secretary also told her there had been "a concerted campaign against" her, and there had been pressure to remove her since 2018.

In an emotional testimony, Ms. Yovanovitch described how she was "shocked and devastated" that a smear campaign against her by Ukrainian officials who were attempting to thwart US anti-corruption policy had found a willing partner in Mr. Trump's personal lawyer Rudy Giuliani. Prior to her removal in May, she was a major force supporting anti-corruption efforts in Ukraine, which helps explain why Trump got rid of her in order to push the quid pro quo, an entry-level move of corrupt politicians.

She denied allegations against her, including that she favored Democrat Hillary Clinton over Trump in the 2016 election, and she rejected the notion that Ukraine tried to interfere in the election, as Trump has claimed counter to mainstream US intelligence findings that it was Russian Federation.

On Wednesday, Taylor offered a new disclosure that indicated Trump's keen interest in the investigations in Ukraine, saying a member of his staff overheard a July 26 phone call at a restaurant in which Trump asked about the probes the president had asked Zelenskiy to conduct a day earlier.

During a long day of testimony, she relayed her striking story of being "kneecapped", recalled from Kyiv by Trump in a swiftly developing series of events that sounded alarms about a White House shadow foreign policy.

Like many others before him, Gordon Sondland, the United States ambassador to the European Union, was appointed to a plum diplomatic post by a grateful president. She already testified in a closed-door meeting with lawmakers about her time as ambassador and her premature recall from her three-year post in Ukraine.

Trump denied the existence of such a call to reporters later Wednesday.

Unabashed, Trump said when asked about it later: "I have the right to speak".

The staffer cited by Taylor is David Holmes, a Taylor aide who has been subpoenaed to testify in the inquiry on Friday behind closed doors, said a person familiar with the issue.