WASHINGTON (WASHINGTON POST) - The United States ambassador to the European Union, Mr Gordon Sondland, intends to tell Congress this week that the content of a text message he wrote denying a quid pro quo with Ukraine was relayed to him directly by President Donald Trump in a phone call, according to a person familiar with his testimony.

Mr Sondland plans to tell lawmakers he has no knowledge of whether the president was telling him the truth at that moment.

"It's only true that the president said it, not that it was the truth," said the person familiar with Mr Sondland's planned testimony, who spoke on the condition of anonymity to discuss sensitive diplomatic matters.

The Sept 9 exchange between Mr Sondland and the top US diplomat to Ukraine has become central to the House Democrats' impeachment inquiry into whether the president abused his office in pressuring Ukraine to open an investigation into his political rival Joe Biden and his son, who sat on the board of a Ukrainian energy company.

The White House and its defenders have held up Mr Sondland's text, which included "no quid pro quo's of any kind", as proof that none was ever considered.

Mr Sondland will hold out the possibility that Mr Trump was not truthful in his denial of a quid pro quo as well as an alternative scenario in which the president's interest in the scheme soured at a time when his administration faced mounting scrutiny over why it was withholding about US$400 million (S$549 million) in security assistance to Ukraine and delaying a leader-level visit with Ukrainian President Volodymyr Zelensky.

"Whether he's deciding it's getting too hot to handle and he backs off whatever his position really was a month earlier, I don't know," the person said of Mr Sondland's understanding.

Hours before Mr Sondland called the president, he received a text message from the acting ambassador to Ukraine, Mr William Taylor, raising questions about the aid holdup.

"I think it's crazy to withhold security assistance for help with a political campaign," Mr Taylor texted Mr Sondland.

That was when Mr Sondland, according to the person's understanding, called Mr Trump, who then told him he didn't "want a quid pro quo...didn't want anything from Ukraine".

The call lasted less than five minutes, and Mr Trump appeared to be in a foul mood, according to the person, who spoke to The Post with Mr Sondland's permission, an intermediary said.

The White House did not respond to a request for comment. Mr Sondland declined to comment through his lawyers.

Mr Sondland, who has emerged as a central actor in Mr Trump's efforts to persuade Ukraine to open investigations, will be deposed before House investigators on Thursday.

Mr Sondland is expected to say that for months before the Sept 9 message, he worked at the direction of Mr Rudy Giuliani, Mr Trump's personal attorney, to secure what he would call in another text message the "deliverable" sought by Mr Trump: a public statement from Ukraine that it would investigate corruption, including mentioning Burisma, a Ukrainian energy company, by name.

In exchange for the statement, the president would grant Ukraine's new president a coveted White House audience.

"It was a quid pro quo, but not a corrupt one," the person familiar with Mr Sondland's testimony said.

Mr Sondland appears poised to say that he and other diplomats did not know that the request to mention Burisma was really an effort to impugn the reputations of Mr Joe Biden and his son Hunter, who had served as a Burisma board member. Mr Sondland contends that he did not know about the Biden connection until a whistle-blower complaint and transcript surfaced in late September.

To trust Mr Sondland's testimony, members of Congress will have to believe Mr Sondland had not seen televised appearances by Mr Giuliani over the spring and summer, or numerous newspaper and magazine articles questioning whether Mr Hunter Biden's role at Burisma could prove to be a drag on his father's presidential campaign.

"If people find that incredulous, it strikes me that the incredulity is hindsight bias," said the person familiar with Mr Sondland's testimony. "The things that seem so clear to people now didn't seem so clear in real time."

The testimony by Mr Sondland, a Portland hotelier who gave US$1 million to Mr Trump's inaugural committee through four of his limited liability companies, could prove damaging to Mr Giuliani and the president.

For months, Mr Sondland's deep involvement in issues related to Ukraine struck diplomats in Brussels and Washington as highly unusual, given his role as envoy to the European Union, a large trade bloc that does not include Ukraine.

Former US officials have said that Mr Sondland viewed the Ukraine assignment as critical to winning Mr Trump's favour and auditioning for a more senior job in the administration.

In Mr Sondland's account, he describes an assignment that begins with excitement and enthusiasm and ends with concern about how the Trump administration was pressing Ukraine, a country fending off Russian-backed separatists that relies heavily on the United States for economic and military support.

Besides working with Mr Giuliani, Mr Sondland also partnered with Mr Kurt Volker, special envoy to Ukraine, and Energy Secretary Rick Perry. The three men were all part of the US delegation to President Zelensky's inauguration in May and left that ceremony excited about the prospects for a vibrant new American partner in Ukraine, according to Mr Sondland's perspective.

The three returned to Washington intent on pressing Mr Trump to meet quickly with Mr Zelensky. But instead of receiving a positive reception, the idea was met with a "buzz saw" in the Oval Office, the person said. Mr Trump was disgruntled about Ukraine, blaming opponents in the country for attempting to undermine his 2016 victory.

The three surmised that Mr Giuliani had filled Mr Trump's head with a number of baseless conspiracy theories, including that a hacked server belonging to the Democratic National Committee was spirited away to Ukraine. Mr Perry, Mr Sondland and Mr Volker each took a turn trying to move Mr Trump to no avail. The president ended the meeting saying: "If you want to do something you have to talk to Rudy."

Mr Volker would take the lead in trying to iron out Mr Giuliani's wishes, starting a three-month exchange of messages over WhatsApp, which were released this month.

Mr Sondland is prepared to say he had a very limited role over the summer. He did not speak directly to Mr Giuliani until Aug 1, the person said. And because of his job in Brussels, he "was not the central connection".

Mr Giuliani, in conversations with The Washington Post, has described Mr Sondland's role as more expansive, saying he spoke with Mr Sondland about six times this summer about Ukraine. "He seemed to be in charge. It just seemed like he was more decisive," Mr Giuliani said.

Mr Giuliani acknowledges seeking a statement in which the Ukrainians would have publicly committed to investigating Burisma, but he says Mr Volker and Mr Sondland drafted it, not him.

Mr Sondland, while acknowledging a close relationship with Mr Trump, viewed Mr Volker as more of a presence on the Ukraine issue. "The fact that he had some relationship with Trump did not put him in the vanguard of dealing with Rudy, that was Volker," the person said.

From May to August, Mr Giuliani's requests for investigations seemed odd but not overly concerning to Mr Sondland, the person said.

"The statement that Rudy was demanding was a quid pro quo for a White House visit, there was no doubt about that. But it was about corruption, which from their perspective wasn't particularly problematic, it's an issue the US had been dealing with there for years."

By Sept 9, Mr Sondland, however, had grown increasingly concerned, as military funding for Ukraine now appeared tied to the statement as well. The person said Mr Sondland was never briefed about Mr Joe Biden being part of the issue and was not aware of it until the transcript of the phone call was released. "If he had known earlier, he never would have touched this."

Some analysts have expressed scepticism that Mr Sondland, who spoke frequently with the president, would not have been read in on why Burisma was of interest to him.

Mr Sondland "somehow wants all of us to believe that he is 'shocked, shocked' that anything he was wrapped up in was aimed at the Bidens. That beggars belief", said Mr Andrew Weiss, vice-president for studies at the Carnegie Endowment for International Peace. "After all, he is a political appointee who prided himself on having direct access to Trump during this period."