(WASHINGTON) Lawmakers will question an official from the U.S. embassy in Ukraine on Thursday as they seek to learn more about a phone call in which he says he overheard President Donald Trump ask about the status of an “investigation” into a political rival.

The public impeachment hearing marks the last scheduled day of marathon sessions by the Democratic-led House Intelligence Committee focused on whether Trump wrongfully pressured Ukraine’s President Volodymyr Zelenskiy to investigate former Vice President Joe Biden, a Democrat bidding to face Trump in the 2020 election.

David Holmes told lawmakers in closed-door testimony that he heard Trump’s voice on a July 26 phone call with Gordon Sondland, the U.S. ambassador to the European Union, in which the Republican president asked about Ukraine’s willingness to carry out an unspecified investigation.

“So, he’s gonna do the investigation?” Trump asked Sondland, referring to Zelenskiy, according to Holmes’ previous testimony.

“He’s gonna do it,” replied Sondland, according to Holmes.

Sondland added the Ukrainian president would do “anything you ask him to,” Holmes said.

Holmes’ account ties Trump directly to an effort to get Ukraine to launch an investigation, though his recounting of the overheard telephone call does not explicitly cite the Bidens.

In his Nov. 15 closed door testimony, Holmes said that after overhearing Sondland’s phone conversation with Trump at an outdoor restaurant in Kiev, he asked the ambassador if it was true that the president did not care about Ukraine.

In Holmes’ telling, Sondland said that it was, and added that Trump only cares about “‘big stuff’ that benefits the President, like the ‘Biden investigation’ that Mr. Giuliani was pushing.”

Testifying before the impeachment inquiry on Wednesday, Sondland said he “followed the president’s orders” to work with Trump’s personal lawyer, Rudy Giuliani, who in turn was pushing Ukraine to carry out two probes that could aid Trump’s 2020 re-election campaign.

The inquiry is focusing on Trump’s request in a July 25 call that Zelenskiy investigate Biden and his son Hunter Biden, who had served on the board of Ukrainian gas company Burisma, and an unsubstantiated theory that Ukraine, not Russia, interfered in the 2016 U.S. election that brought Trump to office.

Trump has denied wrongdoing, verbally assailed witnesses, and described the proceedings as a “witch hunt.” He also says he does not remember the call with Sondland.

Lawmakers on Thursday will also question Fiona Hill, former senior director for European and Russian Affairs on Trump’s National Security Council, who recounted in prior testimony a July 10 meeting in Washington that she attended with senior Ukrainian and U.S. officials at which the investigations were discussed.

Sondland on Wednesday testified he could not remember the precise details of the call Holmes overheard, but said the president’s mention of investigations did not strike him as significant at the time. “Actually, I would have been more surprised if President Trump had not mentioned investigations.”

However, Sondland took issue with Holmes’ recollection that he had talked to the diplomat about the Bidens, saying: “I do not recall mentioning the Bidens. That did not enter my mind. It was Burisma and 2016 elections.”

Sondland has previously testified that he was aware at the time Trump wanted Ukraine to investigate Burisma. But he said he realized only later that such an investigation would involve the Bidens – given Hunter Biden was on Burisma’s board of directors.

He said that several officials at the top of the Trump administration, including Secretary of State Mike Pompeo, were aware of efforts to push Ukraine to launch investigations.

The Trump phone call with Sondland occurred one day after a July 25 conversation between Trump and Zelenskiy that is at the heart of the inquiry into whether Trump misused U.S. foreign policy to his political advantage. Trump asked Zelenskiy to investigate the Bidens on that call.

The inquiry is also looking at whether Trump may have withheld $391 million in security aid to help Ukraine fight Russian-backed separatists in eastern Ukraine as a way of pressuring Kiev to undertake the investigations. Federal law prohibits candidates from accepting foreign help in an election.