In August, Mr. Sondland and the special envoy to Ukraine, Kurt D. Volker, were in negotiations with a top Ukrainian official, Andriy Yermak, about a public statement making a commitment to investigating Mr. Biden and the energy company Burisma, which had placed Mr. Biden’s son Hunter Biden on its board. Mr. Giuliani had been pressing for that commitment and for Mr. Trump’s request that Mr. Zelensky’s government look into whether Ukrainians, not Russians, were behind the hacking of the Democratic National Committee in 2016.
Mr. Sondland and Mr. Volker have testified that they sought to get the Ukrainians to release the statement in order to satisfy Mr. Giuliani and, by extension, Mr. Trump, and to reset relations between the two countries. The Ukrainians never did it.
Mr. Pompeo has said little publicly about what he knew about the pressure campaign on Ukraine, but he has publicly criticized the Democrats’ impeachment investigation, claiming that it has been unfair to Mr. Trump and the State Department. The secretary of state had acceded to Mr. Trump’s order in the spring that he recall the United States ambassador to Ukraine, Marie L. Yovanovitch, who had been the target of a campaign of criticism involving Mr. Giuliani and two of his associates.
While Mr. Pompeo heard Mr. Trump make his demands for the investigations into the Bidens and the 2016 election on the July 25 call with Mr. Zelensky, it is not clear what he knew, or when, about the freeze over the summer of $391 million in United States military aid to Ukraine.
After a meeting on Sept. 1 between Mr. Pence and Mr. Zelensky in Warsaw, Mr. Sondland told Mr. Yermak that the resumption of the aid was tied to an agreement by Ukraine to make a commitment to the investigations sought by Mr. Trump, according to testimony made to the House impeachment inquiry.
Mr. Sondland is one of the few witnesses who spoke directly with Mr. Trump about Ukraine, making his testimony especially important for Democrats. Republicans are expected to try to undercut his credibility by laying out an array of discrepancies in it.
Mr. Sondland initially told the committee that he believed there was no link between the investigations Mr. Trump wanted and the release of the military aid. But two weeks after he was deposed, Mr. Sondland amended his testimony, and said the reverse.