In opening questioning to Mr. Sondland, Mr. Nunes seemed to make the case that Mr. Trump had good reason to seek investigations. He asked Mr. Sondland whether he was aware of a series of facts and various allegations about Hunter Biden and Burisma, and about Ukrainians who expressed support for Hillary Clinton or opposition to Mr. Trump.

“So knowing all these facts from high-ranking Ukrainian officials, ambassador, it probably makes a little more sense now as to why the president may think that there’s problems with Ukraine and that Ukraine was out to get him?” Mr. Nunes asked Mr. Sondland.

“I understand your — I understand your point, yes, Mr. Chairman,” Mr. Sondland replied.

But if the premise of Mr. Nunes’s line of questioning was that it was righteous to seek the investigations, a line of questioning that followed, by the Republicans’ top staff lawyer, Stephen R. Castor, pointed to a different conclusion: The important point was that there was no clear proof that Mr. Trump himself was behind the pressure.

Mr. Castor marched Mr. Sondland through a lengthy series of questions to emphasize the point that Mr. Trump never personally told him there was any quid pro quo — highlighting that Mr. Sondland had no clear proof that the president was personally orchestrating anything untoward.

“So the president never told you about any preconditions for aid to be released?” Mr. Castor asked.

“No,” Mr. Sondland replied.

“The president never told you about preconditions for a White House meeting?” Mr. Castor followed up.

“Personally, no,” Mr. Sondland said.

Mr. Sondland said his understanding that Mr. Trump was offering a White House meeting to Mr. Zelensky on the condition that he announce investigations was based on what Mr. Giuliani told him. Pressed on how he could know that, Mr. Sondland replied that Mr. Trump had directed him to talk to Mr. Giuliani about the matter.