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

In a lengthy opening statement to House investigators, Taylor described the way 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 U.S. 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 back channel to foreign policy, led by the president's personal lawyer Rudy Giuliani and a "weird combination" of "ultimately alarming circumstances" that threaten to erode the United States' relationship with a budding Eastern European ally.

Lawmakers emerging after hours of the private deposition said Taylor relayed a "disturbing" account, including establishing a "direct line" to the quid pro quo at the center of the impeachment probe .

Lawmakers said Taylor recalled events that filled in gaps from the testimony of other witnesses, particularly Ambassador Gordon Sondland, who testified last week and whose statements now are being called into question by Taylor's account. They said Taylor kept records of conversations and documents.

"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."

Taylor's appearance was among the most watched because of a text message, released by House investigators earlier in the probe, in which he called Trump's attempt to hold back military aid to Ukraine "crazy."

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, which was expected to continue into the evening. 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.

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

Taylor laid out the quid pro quo of the White House's decision to withhold military aid to Ukraine unless the new president, Zelenskiy, agreed to Trump's requests to investigate Democrats, according to a person who spoke on the condition of anonymity because the person was not authorized to discuss the private testimony.

In a July phone call, Trump told Zelenskiy he wanted "a favor," 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.

Taylor told lawmakers that another diplomat on the string of text messages, the U.S. ambassador to the European Union, Sondland, was aware of the demands and later admitted he made a mistake that the aid hinged on agreeing to Trump's requests, the person said.

The account calls into question the testimony from Sondland, a wealthy businessman who donated $1 million to Trump's inauguration, who told Congress last week he did not fully remember some details of the events. Sondland may be asked to return to Congress after he testified that, among other things, he was initially unaware that the gas company was tied to the Bidens.

Rep. Ami Bera, D-Calif., said Taylor, a career civil servant, had a better recall of details than Sondland.

Taylor, a retired diplomat, had been chosen to run the Ukraine embassy after the administration abruptly ousted Ambassador Marie Yovanovitch.

In a series of text messages released earlier this month by impeachment investigators, Taylor appeared to be alarmed by Trump's efforts to withhold U.S. military assistance to Ukraine that had already been approved by Congress.

"I think it's crazy to withhold security assistance for help with a political campaign," Taylor wrote in excerpts of the text messages released by the impeachment investigators.

He has stood by that observation in his private remarks to investigators, according to a person familiar with his testimony who was spoke on condition of anonymity to discuss it.

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 his acting chief of staff, Mick Mulvaney, contradicted that last week. Mulvaney later tried to walk back his remarks.

Taylor, a former Army officer, had been serving as executive vice president at the U.S. Institute of Peace, a nonpartisan think tank founded by Congress, when he was appointed to run the embassy in Kyiv. He had served as U.S. ambassador to Ukraine from 2006 to 2009.

"He's the epitome of a seasoned statesman," said John Shmorhun, an American who heads the agricultural company AgroGeneration.

Before retiring from government service, Taylor was involved in diplomatic efforts surrounding several major international conflicts. He served in Jerusalem as U.S. envoy to the Quartet of Mideast peacemakers. He oversaw reconstruction in Iraq from 2004 to 2005, and from Kabul coordinated U.S. and international assistance to Afghanistan from 2002 to 2003.

He arrived in Kyiv a month after the inauguration of Ukraine's new president, prepared to steer the embassy through the transition.

After Trump's phone conversation with Zelenskiy, Taylor exchanged text messages with two of Trump's point men on Ukraine as they were trying to get Zelenskiy to commit to the investigations before setting a date for a coveted White House visit.

In a text message to Sondland on Sept. 1, Taylor bluntly questioned Trump's motives: "Are we now saying that security assistance and WH meeting are conditioned on investigations?" Sondland instructed Taylor to call him. A week later in texts to Sondland and U.S. envoy to Ukraine Kurt Volker, Taylor expressed increased concern and referred to the arrangement as "crazy."

Taylor also texted that not giving the military aid to Ukraine would be his "nightmare" scenario because it would send the wrong message to both Kyiv and Moscow: "The Russians love it. (And I quit)."

U.S. diplomats based at the Kyiv Embassy have refused to speak with journalists, reflecting the sensitivity of the impeachment inquiry. The embassy press office did not respond to a request for comment on Monday.

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Associated Press writers Lynn Berry in Kyiv, Ukraine, and Matthew Lee and Michael Balsamo in Washington contributed to this report.

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Online:

Taylor's opening statement: http://www.documentcloud.org/documents/6509036-Taylor-1.html