US president Donald Trump repeatedly prodded Ukraine's president to look into Democratic rival Joe Biden, according to a rough transcript summarising a call between the two leaders.
In the July 25 call, Mr Trump raised unsubstantiated allegations that the former vice president sought to interfere with a Ukrainian prosecutor's investigation of his son Hunter.
"There's a lot of talk about Biden's son, that Biden stopped the prosecution and a lot of people want to find out about that," Mr Trump said to Ukrainian president Volodymyr Zelenskiy.
As President Trump promised, here is the full, unredacted transcript of his call with the Ukrainian President: https://t.co/XURxHAjTDK
— The White House (@WhiteHouse) September 25, 2019
The conversation between the two leaders is one piece of a whistleblower's complaint, which followed the July 25 call.
The complaint is central to the formal impeachment inquiry launched on Tuesday by House Speaker Nancy Pelosi.
The release of the rough transcript set the parameters of the political debate to come, with Mr Trump dismissing it as routine and Democrats saying it laid the ground for an impeachment inquiry.
Mr Trump aides believed that his oblique, message-by-suggestion style of speaking would not lend itself to the discovery of a "smoking gun" in the transcript.
Mr Trump has recently confirmed that he ordered the freezing of nearly 400 million dollars in aid to Ukraine a few days before the call.
The president has insisted he did nothing wrong and has denied that any request for help in procuring damaging information about Mr Biden was tied to the aid freeze.
The president took the 30-minute call from the White House residence, while officials in the Situation Room listened in and worked to keep a record of the conversation, as is standard practice.
The resulting memorandum was classified as "Secret' and "ORCON, for "originator controlled", to prevent its spread throughout the federal government or to American allies.
It was declassified for release on Wednesday.
The release came against the backdrop of the president presiding over a meeting of world leaders at the United Nations.
"Just so you understand, it's the single greatest witch hunt in American history, probably in history," Mr Trump said during a meeting with foreign leaders in New York.
There has been no President in the history of our Country who has been treated so badly as I have. The Democrats are frozen with hatred and fear. They get nothing done. This should never be allowed to happen to another President. Witch Hunt!
— Donald J. Trump (@realDonaldTrump) September 25, 2019
The inspector general for the intelligence community wrote to the Director of National Intelligence in August that he believed the conversation between Mr Trump and Ukraine's leader could have been a federal campaign finance violation because the president could have been soliciting a campaign contribution from a foreign government, a Justice Department official said.
The whistleblower — a member of the intelligence community — said in their complaint that they had heard the information from "White House officials", but did not have firsthand knowledge of the call, the Justice Department official said.
Prosecutors from the department reviewed a transcript of the call and determined the president did not violate campaign finance law.
The determination was made based on the elements of the allegation, and there was no consideration of the department's policy that a sitting president cannot be indicted, the official said.
Justice Department spokeswoman Kerri Kupec said the attorney general was first notified of Mr Trump's conversation with the Ukrainian president "several weeks after the call took place", when the department received the referral about potential criminal conduct.
"The president has not spoken with the attorney general about having Ukraine investigate anything relating to former Vice President Biden or his son. The president has not asked the attorney general to contact Ukraine on this or any other matter," the spokeswoman said.
— Donald J. Trump (@realDonaldTrump) September 24, 2019
Politicians have been demanding details of the whistleblower's complaint, but the acting director of national intelligence, Joseph Maguire, has refused to share that information, citing presidential privilege.
He is to testify on Thursday before the House, and politicians are expected to have access to details of the complaint beforehand in a classified setting.
The complaint has set off a stunning turn of American political events, leading Ms Pelosi to yield to mounting pressure from fellow Democrats on the impeachment inquiry.
Congress' probe focuses partly on whether Mr Trump abused his presidential powers and sought help from a foreign government to undermine Mr Biden and help his own re-election.
Ms Pelosi said such actions would mark a "betrayal of his oath of office" and declared, "No one is above the law."
Mr Trump has all but dared Democrats to take this step, confident that the spectre of impeachment led by the opposition party will bolster rather than diminish his political support.
Meeting with world leaders at the United Nations, he previewed his defence in an all-caps tweet: "PRESIDENTIAL HARASSMENT!"