WASHINGTON - More than once, U.S. President Donald Trump brought up how much the U.S. has done for Ukraine.

Time and again, he asked Ukraine's president for help.

There was no explicit quid pro quo in Trump's half-hour phone call with Volodymyr Zelenskiy last July. But it wouldn't have been a stretch to make a connection between Trump's pleas for help and his mentions of U.S. assistance.

“We do a lot for Ukraine,†Trump said at one point.

“Do us a favour,†he asked at another.

The White House Wednesday, and it showed that Trump repeatedly prodded Zelenskiy to work with the U.S. attorney general and lawyer Rudy Giuliani to investigate Democratic political rival Joe Biden.

Trump raised allegations, without citing any evidence, that the former vice-president sought to interfere with a Ukrainian prosecutor in regard to son Hunter.

“Whatever you can do with the attorney general would be great,†Trump told Zelenskiy, asking for help in investigating Biden. He referred to Giuliani, his personal attorney and trusted adviser, as a “highly respected man†and said, “I will ask him to call you along with the attorney general.â€

After saying Giuliani and Barr would be in touch, Trump referenced Ukraine's economy, saying: “Your economy is going to get better and better I predict. You have a lot of assets. It's a great country.â€

Zelenskiy had earlier brought up his desire to purchase more Javelin anti-tank missiles from the U.S.

The July 25 conversation between the two leaders is part of a whistleblower's complaint that is central to the formal impeachment inquiry launched Tuesday by House Speaker Nancy Pelosi.

The White House account reveals that Trump was willing to engage a foreign leader to dig up dirt on a political foe and that he went so far as to volunteer his attorney general to help.

Days before the call, Trump froze nearly US$400 million in aid to Ukraine. It was not clear from the summary whether Zelenskiy was aware of that, and the White House did not respond to requests to clarify. The president has insisted he did nothing wrong and has denied that any request for help was tied to the aid freeze.

During a meeting with Trump Wednesday on the sidelines of the UN General Assembly, Zelenskiy said he felt no pressure to act on his call with Trump.

“Nobody pushed me,†he said.

It's illegal under federal law to seek foreign government assistance for U.S. elections.

The release of the rough transcript sets the framework of the political debate to come. Trump, at the U.N. on Wednesday, dismissed it and said as he often does that's he's the victim of “the single greatest witch hunt in American history.†Democrats say it lays the groundwork for the congressional impeachment inquiry.

Trump aides believed that his oblique, message-by-suggestion style of speaking would not lend itself to the discovery of a “smoking gun†in Wednesday's summary. His previous messages to his staff were at the centre of special counsel Robert Mueller's investigation into obstruction of justice in the Trump-Russia case.

Trump's “favour†for Zelenskiy was seeking his help looking into a cybersecurity firm that investigated the 2016 hack of the Democratic National Committee and determined it was carried out by Russia. Trump has falsely suggested Crowdstrike was owned by a Ukrainian.

Then Trump moved to “the other thing†- raising the subject of one of his leading Democratic rivals and a Ukrainian prosecutor: “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.â€

In the conversation, Trump doesn't distinguish between the roles of Giuliani, his personal attorney and political ally, and Barr, who as the nation's top law enforcement officer is meant to be above the political fray. Barr has been a staunch defender of Trump, most notably during the Mueller investigation.

It's not the first time Trump has sought foreign assistance to undermine a political rival. He publicly asked Russia to find missing Hillary Clinton emails in 2016, but this is his first documented time doing so while president with the weight of the U.S. government at his disposal.

The White House did not say whether there are any records of Giuliani's communications with Zelenskiy, nor did it address whether the president's personal attorney learned anything from them. The White House has also not commented on whether Trump discussed Biden on an April 21 call with the Ukrainian leader or with any other foreign power.

The president took the 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. They used voice recognition software, but the call was not recorded. Trump ordered the document declassified Tuesday.

The release came against the backdrop of the president presiding over a meeting of world leaders at the United Nations, a remarkable split screen even for the turbulence of the Trump era.

The inspector general for the intelligence community wrote to the acting Director of National Intelligence in August that he believed the conversation between 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.

The official spoke on condition of anonymity in order to discuss internal investigative deliberations.

Justice Department spokeswoman Kerri Kupec said the attorney general was first notified of 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.

Trump has sought to implicate Biden and his son in the kind of corruption that has long plagued Ukraine.Hunter Biden served on the board of a Ukrainian gas companyat the same time his father was leading the Obama administration's diplomatic dealings with Kyiv. Though the timing raised concerns among anti-corruption advocates, there has been no evidence of wrongdoing by either the former vice-president or his son.

Lawmakers, who have been demanding details of the whistleblower's complaint, were to gain access to the document in a classified setting late Wednesday ahead of the testimony of acting director of national intelligence Joseph Maguire Thursday.

The complaint has set off a stunning turn of American political events, leading Pelosi to yield to mounting pressure from fellow Democrats on the impeachment inquiry.

Trump, who thrives on combat, 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.

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Associated Press Writers Eric Tucker, Lisa Mascaro and Colleen Long contributed to this report.