The whistle-blower, whose identity has not been made public, accused Mr. Trump of abusing his power by inviting a foreign power to interfere on his behalf in the 2020 election. He described the pressure campaign to get Mr. Zelensky to publicly commit to investigations of Democrats that could potentially benefit Mr. Trump and suggested that a temporary hold that the administration had placed on assistance to Ukraine, which is fighting a war against Russian proxy forces, might be related to the effort.

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New details also emerged on Tuesday about that decision to freeze the security assistance to Ukraine. An official from the White House budget office, Mark Sandy, testified that on July 12, he received an email from the office of the acting White House chief of staff, Mick Mulvaney, notifying him that Mr. Trump had directed that administration officials freeze Ukraine’s military aid.

Mr. Trump had enthusiastically sought the investigations for much of the summer. But in early September, he told one of his top diplomats — Gordon D. Sondland, the United States ambassador to the European Union, who helped carry out the shadow policy toward Ukraine — that he was not seeking “a quid pro quo” with the Ukrainian government by withholding the aid.

Mr. Sondland said that when he called Mr. Trump to inquire about why the aid had been withheld, an irritated Mr. Trump insisted he was not seeking anything from the Ukrainians. But the president said that he wanted Mr. Zelensky “to do the right thing,” Mr. Sondland testified to Congress last week, suggesting that he was still seeking the investigations into Democrats that could help his political fortunes.

There are discrepancies about whether Mr. Sondland spoke to the president on Sept. 7 or 9. The administration lifted the freeze on aid to Ukraine on Sept. 11, as lawmakers’ demands grew. Two days earlier, three Democratic-led House committees had opened an investigation into Mr. Trump’s dealings with Ukraine.

Only days after the president learned of the whistle-blower complaint, he spoke with Senator Ron Johnson, Republican of Wisconsin, about the aid holdup. Mr. Johnson sought permission to tell Mr. Zelensky at an upcoming meeting in Ukraine that Mr. Trump had decided to release the security assistance, according to Mr. Johnson.

Mr. Trump replied that he was not ready, Mr. Johnson said. He said he asked later on the call whether the aid was linked to some action that the president wanted the Ukrainians to take.