Washington, Oct 23 (AP) Former US Ambassador William Taylor provided lawmakers Tuesday with a vivid, detailed and what some called a "disturbing" account of the way President Donald Trump wanted to put the new Ukraine president "in a public box" by demanding the quid pro quo at the centre of the impeachment probe.

In a lengthy opening statement to House investigators, Taylor described Trump's demand that "everything" Ukrainian President Volodymyr Zelenskiy wanted, including vital military aid to counter Russia, hinged on making a public vow that he would investigate Democrats going back to the 2016 US election as well as a company linked to the family of Trump's potential 2020 Democratic rival Joe Biden.

Taylor testified that what he discovered in Kyiv was the Trump administration's "irregular" back channel to foreign policy led by the president's personal lawyer, Rudy Giuliani, and "ultimately alarming circumstances" that threatened to erode the United States' relationship with a budding Eastern European ally.

Lawmakers who emerged after hours of the private deposition were stunned at Taylor's account, which some said established a "direct line" to the quid pro quo at the center of the impeachment probe.

"It was shocking," said Rep. Karen Bass, a California Democrat. "It was very clear that it was required — if you want the assistance you have to make a public statement." She characterized it as, "It's this for that." Rep. Dina Titus, a Democrat from Nevada, said, "You can see how damning this is."

Titus said, "This certainly makes it pretty clear what was going on. And it was a quid pro quo." The account reaches to the highest levels of the administration, drawing in Vice President Mike Pence and Trump's acting chief of staff Mick Mulvaney, and slices the core of Republican defence of the administration and president's insistence of no wrongdoing.

It lays bare the struggle between former National Security Adviser John Bolton and those who a previous witness described as the "three amigos" — Giuliani and two other diplomats — who were leading an alternative Ukraine policy vis-a-vis Russia.

Taylor's appearance was among the most anticipated before House investigators because of a series of text messages in which he called Trump's attempt to hold back military aid to Ukraine "crazy." His testimony opens a new front in the impeachment inquiry, and it calls into question the account from another diplomat, Gordon Sondland, the US ambassador to the European Union, who told Congress last week he did not fully remember some details of the events and was initially unaware that the gas company was tied to the Bidens.

Taylor told lawmakers that Sondland, a wealthy businessman who donated USD 1 million to Trump's inauguration, was aware of the demands and later admitted he made a mistake by telling the Ukrainians that military assistance was not contingent on agreeing to Trump's requests.

"Ambassador Sondland told me that President Trump had told him that he wants President Zelenskyy to state publicly that Ukraine will investigate Burisma and alleged Ukrainian interference in the 2016 US election," Taylor said about a September 1 phone call between them.

Taylor apparently kept detailed records of conversations and documents, lawmakers said.

The retired diplomat, a former Army officer, had been serving as executive vice president at the US Institute of Peace, a nonpartisan think tank founded by Congress, when he was appointed to run the embassy in Kyiv after Trump suddenly recalled Ambassador Maria Yovanovitch.

Taylor testified that he had concerns about taking over the post under those circumstances, but she urged him to go "for policy reasons and for the morale of the embassy." He had served as US ambassador to Ukraine from 2006 to 2009.

Lawmakers described the career civil servant's delivery as credible and consistent, as he answered hours of questions from Democrats and Republicans, drawing silence in the room as lawmakers exchanged glances.

Taylor testified that he "sat in astonishment" on a July 18 call in which a White House budget official said that Trump had relayed a message through Mulvaney that the aid should be withheld.

A month later, his concerns had so deepened he was preparing to resign. Sensing the US policy toward Ukraine has shifted, he described an August 22 phone call with Tim Morrison, a Russia adviser at the White House, who told him, the "president doesn't want to provide any assistance at all." "That was extremely troubling to me," Taylor said.

Taylor's description of Trump's position is in sharp contrast to how the president has characterized it. Trump has said many times that there was no quid pro quo, though Mulvaney contradicted that last week. Mulvaney later tried to walk back his remarks. "The testimony is very disturbing," said Rep. Carolyn Maloney, D-N.Y. Rep. Dean Phillips, D-Minn., used the same word. Asked why, he said, "Because it's becoming more distinct." Rep. Debbie Wasserman Schultz, D-Fla., said Taylor "drew a straight line" with documents, timelines and individual conversations in his records.

"I do not know how you would listen to today's testimony from Ambassador Taylor and come to any other (conclusion) except that the president abused his power and withheld foreign aid," she said.

Lawmakers did not discuss other details of the closed-door session, and Taylor declined to comment as he entered the deposition. He was the latest diplomat with concerns to testify. Like the others, he was subpoenaed to appear.

In a July phone call, Trump told Zelenskiy he wanted "a favour," which the White House later acknowledged in a rough transcript of the conversation was Trump's desire for Ukraine to investigate the Democratic National Committee's email hack in 2016 as well as a Ukrainian gas company, Burisma, with ties to Biden's family. (AP)

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