In a 15-page opening statement quickly leaked to US media, Bill Taylor recounted in deep detail how Ukraine's new president, Volodymyr Zelenskiy, came under sustained pressure after taking office.
The top US diplomat in Ukraine poured fuel on Donald Trump's impeachment probe Tuesday with a detailed account of how the president pushed Kiev to discredit one of his main political rivals, withholding US military aid to exert pressure.
Democrats said the congressional testimony by Bill Taylor was a stunning confirmation of their allegations that Trump abused his office by seeking foreign help to hurt Democratic candidate Joe Biden in the 2020 presidential election.
"It's all there. What's there left for me to say when you have such a clear and detailed statement?" said House Democrat Tom Malinowski, a former diplomat.
Senior Republicans had no immediate response but the White House rejected what it called a "coordinated smear campaign from far-left lawmakers and radical unelected bureaucrats."
"Today was just more triple hearsay and selective leaks from the Democrats' politically-motivated, closed-door, secretive hearings," the administration said in a statement.
"Every day this nonsense continues more taxpayer time and money is wasted."
In a 15-page opening statement quickly leaked to US media, Taylor recounted in deep detail how Ukraine's new president, Volodymyr Zelenskiy, came under sustained pressure after taking office.
Taylor said he was told Trump wanted Zelenskiy "to state publicly" that he would investigate Biden and his son Hunter for what he said was corruption in the ex-Soviet republic.
He said that the US ambassador to the European Union, Gordon Sondland, told him that "'everything' was dependent on such an announcement, including security assistance."
Another carrot being dangled, Taylor said, was a proposed summit between Zelenskiy and Trump.
Emerging from the testimony, Democratic congressman Adriano Espaillat tweeted that "what I heard today from #BillTaylor was very troubling and explosive."
"At some point we're going to have to conclude our investigation and go forward with what we have, and what we have is incredibly damning right now," another Democratic legislator, Ted Lieu, said.
A new CNN/SSRS poll on Tuesday showed support for Trump's removal from office is now 50 percent to 43 against.
However, reflecting the intensely partisan divide among voters, 87 percent of Democrats are pro-impeachment, compared to just six percent of Republicans.
Trump admits to asking Ukraine's government to probe what he says is corruption related to Biden.
However, he denies Democrats' allegation that he tried to strong-arm the Ukrainians by linking the delivery of US military aid to his request for an investigation.
Trump has already branded the impeachment proceedings a "coup," a "hoax," a "witch hunt" and a variety of swear words.
On Tuesday, he prompted an uproar by claiming he was the victim of a lynching, a word linked in the United States to the darkest days of slavery's aftermath.
"All Republicans must remember what they are witnessing here — a lynching," Trump tweeted.
More than 3,400 African Americans were lynched between 1882 and 1968, and congressional Democrats reacted with collective anger.
"How dare you?!" seethed congresswoman Barbara Lee on Twitter as she assailed the "disgusting and ignorant message" from Trump.
How dare you?! Since the founding of our nation, African Americans have been lynched and killed just for being black.— Rep. Barbara Lee (@RepBarbaraLee) October 22, 2019
This is a disgusting and ignorant message from a man who has shown no respect for history. We will not stand for it. pic.twitter.com/2d1Jin5gHP
The White House fought back, with spokesman Hogan Gidley insisting that Trump did not mean to compare "what's happened to him to one of the country's darkest moments."
There was rare criticism from the top Republican legislator, Senator Mitch McConnell, who said Trump had made "an unfortunate choice of words."
He added, however, that Trump does have a "legitimate complaint" over a "totally unfair process."
Trump will rely on McConnell to deliver an acquittal in the Senate if the lower house does go ahead with an impeachment vote.
Trump did urge Zelenskiy in July to investigate Biden and his son, according to a summary of a phone call released by the White House.
Seeking help from a foreign country in a domestic election is illegal in itself, but a whistleblower complaint about the call made the more serious allegation that Trump also sought to condition nearly $400 million in military aid to Ukraine on Kiev launching a probe.
Taylor is a military veteran and career diplomat who served as US ambassador to Ukraine from 2006 to 2009 and is now charge d'affaires following the ouster of ambassador Marie Yovanovitch this year.
Yovanovitch testified to Congress two weeks ago, telling House investigators she was pushed out on "false claims" that she had disparaged Trump.
According to Taylor, much of the pressure he described was applied through "weird" back channels, including Trump's personal lawyer Rudy Giuliani.
Taylor had already damaged Trump's defence with a paper trail that included text messages in which he expresses alarm about having to pressure Zelenskiy's government.
"Are we now saying that security assistance and WH (White House) meeting are conditioned on investigations?" Taylor asked Sondland in a September text message.
Later, Taylor expressed more explicit reservations to Sondland: "I think it's crazy to withhold security assistance for help with a political campaign."
On Tuesday, Taylor said in his opening statement that he stood by that characterisation of the quid pro quo being "crazy."