WASHINGTON (Reuters) - The top American diplomat in Ukraine testified on Tuesday that President Donald Trump made the release of U.S. security aid to Ukraine contingent on Kiev publicly declaring it would carry out politically motivated investigations that he demanded.

The comments by William Taylor, a career diplomat and former Army officer who serves as the charge d’affaires in the U.S. embassy in Ukraine, were in a copy of his statement to lawmakers posted online by U.S. media.

Taylor’s statement to the three Democratic-led House of Representatives committees leading an impeachment inquiry against the Republican president marked a pivotal development in the political drama unfolding in Washington that threatens Trump’s presidency even as he pursues re-election.

It ran counter to Trump’s contention that there was no quid pro quo - a Latin phrase meaning a favor for a favor - related to the $391 million in security assistance approved by the U.S. Congress to help combat Russia-backed separatists in eastern Ukraine that Trump had withheld.

“It was the most damning testimony,” Democratic Representative Debbie Wasserman Schultz told Reuters.

In closed-door testimony, Taylor said he was told by Gordon Sondland, the U.S. envoy to the European Union, that Trump had linked release of the aid to public declarations by Ukrainian President Volodymyr Zelenskiy that he would investigate Trump’s domestic political rival Joe Biden, and his son Hunter Biden, as well as a debunked conspiracy theory about the 2016 election.

Zelenskiy agreed to the request. The aid was later released.

“There was no quid pro quo,” said White House spokeswoman Stephanie Grisham. “Today was just more triple hearsay and selective leaks from the Democrats’ politically-motivated, closed door, secretive hearings.”

In his testimony, Taylor detailed numerous conversations and events and emphasized the strategic importance of Ukraine as it faces Russian aggression.

Previously released text messages that Taylor sent to other senior U.S. officials denounced as “crazy” the idea of withholding the security aid to benefit a domestic political campaign.

In his testimony, Taylor emphatically reiterated that view.

The House inquiry is focusing on Trump’s request during a July 25 telephone call with Zelenskiy that he investigate the Bidens.

Former Vice President Joe Biden is a leading contender for the 2020 Democratic presidential nomination to face Republican Trump. Hunter Biden had served on the board of Ukrainian energy company Burisma.

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Taylor said Trump also made a White House invitation to Zelenskiy contingent on announcing the investigations.

The content of the phone call was first revealed by a whistleblower within a U.S. intelligence agency, who submitted a report saying Trump pressured Zelenskiy to advance his personal political interests.

Trump also publicly asked China to investigate the Bidens.

Federal election law prohibits candidates from accepting foreign help in an election.

‘DIRECT LINE’

Wasserman Schultz said Taylor “drew the most direct line that I’ve heard from President Trump to the withholding of foreign aid to a vital diplomatic partner ... and tying the withholding of that funding and the meeting that President Zelenskiy wanted to President Zelenskiy declaring that he would open investigations into the Burisma Biden issue and the 2016 election.”

Trump has denied any quid pro quo or wrongdoing and accused Democrats of trying to oust him to prevent him from being re-elected.

However, his acting chief of staff last week acknowledged that the aid was contingent on Ukraine investigating a discredited theory that there is a Democratic National Committee (DNC) computer server in Ukraine.

In his opening statement, Taylor said, “Ambassador Sondland told me that President Trump had told him that he wants President Zelenskiy to state publicly that Ukraine will investigate Burisma and alleged Ukrainian interference in the 2016 election.”

The “alleged Ukrainian interference” is a reference to a debunked conspiracy theory that it was Ukraine, and not Russia, that interfered in the 2016 U.S. election.

U.S. intelligence agencies and a special counsel investigation concluded that Russia used a campaign of hacking and propaganda to undermine Democratic candidate Hillary Clinton and boost Trump’s candidacy in 2016.

Taylor had mentioned his concerns over the withholding of U.S. aid on Sept. 9 to Sondland and Kurt Volker, the State Department’s former special envoy to Ukraine, in a text message provided to House investigators and later made public.

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“As I said on the phone, I think it’s crazy to withhold security assistance for help with a political campaign,” Taylor wrote in the text message.

‘A RANCOROUS STORY’

On Tuesday, Taylor told lawmakers that Trump’s administration had established an “irregular, informal channel of U.S. policy-making” that ran counter to stated diplomatic goals.

Taylor described this channel as including Trump’s personal lawyer Rudy Giuliani, then-Special Envoy to Ukraine Kurt Volker, Energy Secretary Rick Perry and Sondland.

“It is a rancorous story about whistleblowers, Mr. Giuliani, side channels, quid pro quos, corruption, and interference in elections,” Taylor testified.

Taylor also said Sondland told him that he recognized he had made a mistake by earlier telling Ukrainian officials that Zelenskiy’s desire for a White House meeting with Trump was dependent on a public announcement of investigations Trump sought.

In fact, Taylor testified, Sondland said, “‘Everything’ was dependent on such an announcement, including security assistance.”

Taylor was tapped to serve as charge d’affaires in Kiev, where he had served as U.S. ambassador from 2006 to 2009, after Trump in May abruptly removed Ambassador Marie Yovanovitch. Giuliani had portrayed her as resisting his efforts to push Ukraine to investigate the Bidens.

Yovanovitch testified in the impeachment inquiry on Oct. 11.

Sondland was a wealthy Oregon hotelier and Trump political donor named to his European diplomatic post last year.

In his testimony to lawmakers, he expressed concern that Trump had ordered U.S. officials in May to work with Giuliani on Ukraine policy. Giuliani had been working to engineer a Ukrainian investigation of the Bidens.

Taylor said Sondland, during a Sept. 8 phone call, “tried to explain to me that President Trump is a businessman. When a businessman is about to sign a check to someone who owes him something, he said, the businessman asks that person to pay up before signing the check.”

In addition, Taylor said Volker used the same terms days later.

“I argued to both that the explanation made no sense: The Ukrainians did not ‘owe’ President Trump anything, and holding up security assistance for domestic political gain was ‘crazy,’ as I had said in my message to Ambassadors Sondland and Volker on September 9,” Taylor testified.

Democratic Representative Gerry Connolly told reporters Taylor’s testimony was based on meticulous contemporaneous notes of conversations and meetings, adding to his credibility as a witness.

(Graphic: The impeachment inquiry, here)