Watch: Gordon Sondland testifies in pivotal fourth day of Trump public impeachment hearings

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The fourth round of public impeachment hearings begins with Gordon Sondland, the U.S. ambassador to the European Union, who is slated to testify before the House Intelligence Committee on Wednesday morning.

It is likely to be the most pivotal testimony yet in the House impeachment investigation into whether President Donald Trump abused his power by pressuring Ukraine President Volodymyr Zelenskiy to open probes into Trump's political rivals.

Intelligence Committee Chairman Adam Schiff, D-Calif., and the Democrats' counsel, Daniel Goldman, will likely ask Sondland about revelations of a phone call between the ambassador and Trump. David Holmes, an embassy official in Kyiv, testified in a closed-door deposition that he overheard a July 26 conversation between Trump and Sondland, a day after Trump asked Zelenskiy to "look into" unsubstantiated allegations about former Vice President Joe Biden and his son Hunter, and a conspiracy theory regarding the 2016 election.

In the call, according to Holmes, Trump asked whether Zelenskiy is "going to do the investigation." Sondland told the president that Zelenskiy is "going to do ... anything you ask him to," according to Holmes' testimony. Holmes is slated to testify in public Thursday.

Sondland had not disclosed his July 26 call with Trump in previous private testimony with the committee.

Earlier this month, Sondland revised a statement he gave in a private deposition and said he did tell a Ukrainian official that Trump would not release $400 million in military aid unless Ukraine agreed to open investigations into Biden, a front-runner in the 2020 Democratic presidential race.

Read more: Trump ambassador changes testimony, admits telling Ukraine there would be no US aid without investigations

Sondland submitted the revised statement in a four-page document a day before the House released the entire testimony. He attributed his recollection to testimony from other administration officials — who contradicted Sondland's original testimony.

Two more witnesses — Defense Department official Laura Cooper and State Department official David Hale — are scheduled to appear together at the hearing Wednesday afternoon.

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