Bill Taylor, the US's chief envoy to Ukraine, gave "damning" testimony to Congress on Tuesday that prompted "sighs and gasps" from people in the room, The Washington Post and Politico reported.

Taylor implicated President Donald Trump for directing the US to withhold security assistance from Ukraine unless they caved to his demands for politically motivated investigations.

He also gave testimony that appears to be at odds with what Gordon Sondland, the US's ambassador to the European Union, told lawmakers last week. One Democratic congressman said it was possible Sondland could be facing a perjury charge in light of Taylor's remarks.

Scroll down to read what Taylor revealed to Congress during his bombshell testimony.

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Bill Taylor, the US's acting ambassador to Ukraine, gave "damning" testimony Tuesday about what lawmakers said were President Donald Trump's efforts to withhold military aid to Ukraine in exchange for politically motivated investigations, The Washington Post reported.

Taylor has firsthand knowledge about efforts by two other diplomats — Gordon Sondland and Kurt Volker — to help Trump and his personal lawyer Rudy Giuliani push the Ukrainian government to launch politically motivated investigations that would benefit Trump at the same time the US was withholding military aid to Ukraine.

Politico reported on Tuesday that Taylor's 15-page opening statement prompted "sighs and gasps" from people in the room as he read aloud from it. Speaking with Politico, another person in the room described Taylor's statement as showcasing "how pervasive the efforts were" among Trump's allies to push Ukrainian government officials to investigate former Vice President Joe Biden and his son, and help discredit the FBI's Russia investigation.

Here's what Taylor revealed to Congress, according to his opening statement:

There were two channels of US foreign policy: an official one and an unofficial one

Once he took over for Marie Yovanovitch as acting ambassador to Ukraine and arrived in the country's capital, Kyiv, Taylor noticed "a weird combination of encouraging, confusing, and ultimately alarming circumstances."

Zelensky was in an unusual hurry to take over the country's government after winning the election.

There was a "confusing and unusual" way US policy toward Ukraine was conducted: There appeared to be two channels, one official and one unofficial.

Taylor was in charge of the official channel, which included formal diplomatic processes, helping Ukraine fight Russian aggression, and helping to fight corruption.

The "irregular" and unofficial channel involved Giuliani, Volker, Sondland, and Energy Secretary Rick Perry. The unofficial channel began when Volker, Sondland, Perry, and Sen. Ron Johnson returned from Zelensky's inauguration on May 23.

At first, both channels shared similar goals, but they soon "diverged in their objectives," which "deeply concerned" Taylor.

Sondland tells Taylor that Trump wants Zelensky's assurance that he won't get in the way of 'investigations'

In June, both channels had the goal of arranging a White House meeting between Trump and Zelensky. But on June 27, Sondland told Taylor that the US president wanted Zelensky's assurance that he would not stand in the way of "investigations" Trump wanted.

On June 28, Taylor grew concerned when Sondland told him he didn't want most of the normal interagency participants in on a call planned with Zelensky later that day. Only Taylor, Sondland, Volker, and Perry participated in the call.

Sondland also said he wanted to make sure no one was transcribing or monitoring the call.

Before Zelensky joined the call, Volker told the other US participants that he planned to be explicit and tell the Ukrainian president that Trump wanted him to cooperate with "investigations" and "get to the bottom of things" in order to secure a White House meeting.

Taylor reported on the call to Deputy Assistant Secretary of State George Kent and created a contemporaneous memo documenting the conversation and the phone call on June 30.

Taylor learned that a Trump-Zelensky White House meeting was conditioned on investigations that would help Trump's campaign

It became clear to Taylor by mid-July that the White House meeting was conditioned on Zelensky investigating Burisma Holdings, the Ukrainian natural-gas company whose board Hunter Biden sat on until recently, and alleged Ukrainian interference in the 2016 US election.

Taylor understood that this condition was driven by the unofficial channel spearheaded by Giuliani.

On July 10, Ukrainian officials — including the Zelensky aide Andriy Yermak — met at the White House with Perry, Sondland, Volker, and then-national security adviser John Bolton.

The same day, Taylor met in Kyiv with Andriy Bohdan, Zelensky's chief of staff, and Vadym Prystaiko, Ukraine's foreign minister. The two men told Taylor that Giuliani had told them a phone call between Trump and Zelensky was unlikely, and that they were "alarmed and disappointed."

Taylor was 'astonished' when he found out in July the US was withholding military aid to Ukraine

On July 18, Taylor learned during a regular National Security Council video call that the US was withholding security assistance from Ukraine. A voice on the call said she had been instructed by her boss to hold the aid until further notice.

The person, who was off screen, said the directive came from Trump to Mick Mulvaney, his acting chief of staff, to the Office of Management and Budget.

Taylor and others on the call "sat in astonishment."

It was at this point that Taylor realized one of the "key pillars" of US support for Ukraine was under threat and that the unofficial policy channel was "running contrary to the goals of longstanding US policy."

After the phone call, the NSC led a series of interagency meetings that included everyone from staff to cabinet secretaries. The goal of the meetings was to determine the usefulness of US military aid to Ukraine.

At every meeting, the "unanimous conclusion" was that Ukraine should get the aid, and the Department of Defense even submitted an analysis that found the assistance was "effective and should be resumed."

Taylor's understanding was that several cabinet secretaries and top government officials — including Bolton, Secretary of Defense Mark Esper, Secretary of State Mike Pompeo, and CIA Director Gina Haspel — wanted a joint meeting with Trump to convince him to resume Ukraine's military aid. But the meeting was hard to schedule.

Taylor learned Bolton was against Trump having a phone call with Zelensky because he believed it 'would be a disaster'

The next day, on July 19, Fiona Hill, the White House's senior director for Russian and Eurasian affairs, and Alex Vindman, the NSC's director of European affairs, spoke with Taylor on the phone and told him they weren't aware of any official change in US policy toward Ukraine.

Hill and Vindman told Taylor about the July 10 meeting and said Sondland had tied "investigations" to an Oval Office meeting between Trump and Zelensky. The conversation irritated Bolton so much that he left and said Sondland, Volker, and Perry should have nothing to do with domestic politics.

Bolton also told Hill to "brief the lawyers" on what had happened at the White House meeting between Sondland, Volker, Perry, and Ukrainian officials.

Bolton was against Trump and Zelensky having a phone call because he believed it "would be a disaster."

Ukrainians in the White House meeting were confused because the people representing the official and unofficial foreign-policy channels wanted two different things: Bolton wanted to discuss energy, security, and reform, while Sondland wanted to discuss how investigations were a precondition for a White House meeting between Trump and Zelensky.

Hill told Taylor that Volker met with Giuliani to discuss Ukraine, which concerned Taylor because he further sensed that the two channels were at odds.

Taylor began texting with Volker and Sondland on July 19 amid growing concerns about their shadow foreign-policy campaign

Taylor began exchanging texts with Volker and Sondland beginning on July 19, and both men emphasized Trump's desire that Zelensky pursue "investigations" that would benefit the US president.

Taylor had a conversation with a top Ukrainian official on July 20, during which the official told Taylor that Zelensky didn't want to be a pawn in US political campaigns.

On July 25, after Trump's call with Zelensky, Taylor did not receive a White House memo of the conversation.

On July 26, Zelensky told Volker and Taylor he was happy with the conversation but didn't elaborate.

On July 28, Hill's replacement, Tim Morrison, told Taylor the phone call "could have been better" and that Trump had told Zelensky to work with Giuliani and Attorney General Bill Barr.

On August 16, Volker texted Taylor to tell him that Yermak had asked the US to submit an official request for Ukraine to investigate whether Burisma violated Ukrainian laws. Taylor thought a formal US request for Ukraine to look into violations of its own laws was improper and told Volker to "stay clear."

Taylor prepared to resign and said he wouldn't defend a US policy that withheld aid to Ukraine

By mid-August, Taylor's concerns about the US withholding aid deepened. They were exacerbated further when Taylor asked Morrison about the status of the assistance on August 22, and Morrison replied that "it remains to be seen" and that Trump "does not want to provide any assistance at all."

Taylor was so alarmed by the call with Morrison that he prepared to resign.

On August 27, Bolton traveled to Kyiv to meet with Zelensky. Near the end of Bolton's visit, Taylor met with him and expressed his "serious concern" about withholding military aid. Bolton told Taylor to relay his concerns to Pompeo.

On August 29, Taylor contacted Pompeo via a "first-person cable" and told him of the "folly" in holding up aid. He said he would not defend a US policy that withheld security assistance to Ukraine as it fought off Russian aggression.

That same day, Yermak contacted Taylor and said he was very concerned the US was withholding aid. The decision had been made public that same day in a Politico story (the Ukrainians were not aware of it before then).

Taylor was "embarrassed" that he couldn't give Yermak an appropriate reason for why the aid was stalled.

Taylor was 'alarmed' when he first found out that Trump was explicitly tying the aid to his demand for investigations

On September 1, Morrison told Taylor during a phone call that Sondland had told Yermak the US would not provide aid unless Zelensky committed to pursuing an investigation into Burisma.

The revelation "alarmed" Taylor, who began to understand that the aid was being tied to "investigations" Trump wanted.

The same day, Taylor texted Sondland: "Are we now saying that security assistance and WH meeting are conditioned on investigations?"

Sondland: 'Everything' — including military aid — depends on Zelensky publicly committing to the investigations Trump wanted

Sondland told Taylor to call him. During their conversation, Sondland said Trump told him he wanted Zelensky to publicly commit to investigating Burisma and alleged Ukrainian interference in the 2016 US election.

Sondland also told Taylor he made a mistake when he told Ukrainian officials that a Trump-Zelensky White House meeting depended on Zelensky publicly committing to the investigations.

Instead, Sondland said, "everything" — including security assistance — depended on that.

Sondland told Taylor Trump wanted to put Zelensky "in a public box" by making a statement ordering the investigations Trump wanted.

Taylor told Sondland that Trump should have more respect for Zelensky and that what Trump was asking for wasn't in the US's or Ukraine's interest. He asked Sondland to push back on Trump's demand. Sondland said he would try.

On September 2, Morrison told Taylor US officials were bothered by their inability to answer Ukrainian officials' questions about why the aid was being withheld. Taylor was experiencing the same tensions, and he also briefed Morrison on his earlier conversation with Sondland.

On September 5, US Sens. Johnson and Chris Murphy visited Ukraine and met with Zelensky. Zelensky's first question to them was about the security assistance.

The senators told Zelensky he should not jeopardize the US's bipartisan support for Ukraine by getting involved in domestic politics.

Taylor emphasized to Ukrainian officials that the push to make Zelensky publicly commit to investigating Burisma and the 2016 election "showed how the official foreign policy of the United States was undercut by the irregular efforts led by Mr. Giuliani."

Trump told Sondland he wasn't looking for a quid pro quo, right before asking for a quid pro quo

On September 7, Taylor had a conversation with Morrison in which Morrison said he had a "sinking feeling" about a separate conversation Sondland had with Trump earlier that day.

According to Morrison, Trump told Sondland he wasn't asking for a quid pro quo. But then he insisted that Zelensky go out in public and say he was launching an investigation into Biden and the 2016 election.

Morrison told Taylor he informed NSC lawyers of the phone call between Sondland and Trump during which Trump conveyed the above sentiments.

On September 8, Sondland told Taylor he had spoken with Trump but that Trump was adamant Zelensky "clear things up and do it in public."

Sondland conveyed to Taylor that Trump said it wasn't a quid pro quo, but that if Zelensky didn't "clear things up" publicly, they would be at a "stalemate." Sondland said his conversation ended with Zelensky agreeing to make a public statement in a CNN interview.

Taylor understood "stalemate" to mean that Ukraine would not get the security assistance.

After the September 8 conversation, Taylor texted Sondland saying his "nightmare is they give the interview and don't get the security assistance. The Russians love it. (And I quit.)."

"I was serious," Taylor testified of his sentiments.

Sondland and Volker tried arguing that Trump is a businessman who Ukraine 'owes' and that he wants Ukraine to 'pay up' before the US gives military aid. Taylor told them that was 'crazy.'

The next day, Taylor texted Volker and Sondland and told them Ukraine's "faith" in the US was "shaken" and that it was "crazy" to withhold security assistance for "help with a political campaign."

Sondland replied five hours later and said Taylor was wrong about his interpretation of the situation and that Trump had been clear that there was no quid pro quo involved.

Before those texts were exchanged, Taylor said Sondland tried to explain to him that Trump "is a businessman" and "when a businessman is about to sign a check to someone who owes him something ... the businessman asks that person to pay up before signing the check."

Volker tried making the same argument a few days later, which Taylor again shot down as "crazy."

Taylor said Ukraine didn't "owe" Trump anything.

US finally lifted the hold on military aid on September 11