President Donald Trump has insisted there was no "quid pro quo" in his dealings with the Ukrainian government, and "no pressure" on Ukraine's president to open an investigation into former Vice President Joe Biden and his son.

But in his remarkable 15-page statement delivered to Congress on Tuesday, Trump's top diplomat to Ukraine painted a picture of both.

"I do not know how you would listen to today's testimony by the ambassador, Ambassador Taylor, and draw any other conclusion, except that the president abused his power and withheld foreign aid," said Rep. Debbie Wasserman Schultz, D-Fla. "It's a direct line."

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Rep. Adriano Espaillat, D-N.Y., referred to the testimony as "explosive."

Here are six of the statement's most astonishing scenes described in Taylor's testimony, which may become a milestone in the Democrats' impeachment inquiry:

1. Taylor details 'highly irregular' backchannel

Taylor, who was ambassador to Ukraine during the Bush administration, returned to service to replace Marie Yovanovitch, who was recalled from the position in May. Taylor said that Secretary of State Mike Pompeo assured him at the time that the U.S. "policy of strong support for Ukraine would continue and that he would support me in defending that policy."

"But once I arrived in Kyiv, I discovered a weird combination of encouraging, confusing, and ultimately alarming circumstances," Taylor wrote in his statement.

"I found a confusing and unusual arrangement for making U.S. policy towards Ukraine. There appeared to be two channels of U.S. policy-making and implementation, one regular and one highly irregular."

The "irregular, informal channel" included then-Special Envoy Kurt Volker, European Union Ambassador Gordon Sondland, Energy Secretary Rick Perry and Trump's personal lawyer, Rudy Giuliani.

"The push to make President Zelenskiy publicly commit to investigations of Burisma and alleged interference in the 2016 election showed how the official foreign policy of the United States was undercut by the irregular efforts led by Giuliani," Taylor added later.

2. Taylor describes when he learned about the Ukraine aid hold

On July 10, Taylor said he was told by a Ukrainian official that Giuliani had informed him that a planned phone call between Trump and new Ukraine president Volodomyr Zelenskiy was "unlikely to happen." A week later, Taylor heard from an Office of Management and Budget staffer in a National Security Council conference call that a hold has been placed on Ukraine aid.

"All that the OMB staff person said was that the directive had come from the president to the chief of staff to OMB. In an instant, I realized that one of the key pillars of our strong support for Ukraine was threatened," Taylor wrote.

He said he later found out that in a meeting with Ukrainian officials and NSC staffers that Sondland "had connected 'investigations' with an Oval Office meeting for President Zelenskiy."

3. A Ukrainian official tells Taylor that Zelenskiy 'did not want to be used as a pawn'

As Taylor kept working to set up the call between the two leaders, he said "Sondland told me that he had recommended to President Zelenskiy that he use the phrase, 'I will leave no stone unturned' with regard to 'investigations' when they speak."

A Ukrainian official told Taylor that Zelenskiy "did not want to be used as pawn in the U.S. re-election campaign," a concern Taylor passed on to Sondland and Volker.

Trump said he and Zelenskiy spoke five days later. "I received no readout of the call from the White House," Taylor said.

4. Taylor says it became clear to him that the aid freeze was tied to the Biden probe

Ukrainian officials found out about the hold on aid on Aug. 29, after an article appeared in Politico.

"It had still not occurred to me that the hold on security assistance could be related to the 'investigations.' That, however, would soon change," Taylor wrote.

In early September, Taylor said he spoke with an NSC official who described a conversation Sondland had with a Ukrainian official at an event in Poland. Sondland told the official "the security assistance money would not come until President Zelenskiy committed to pursue the Burisma investigation" — a reference to the company Hunter Biden was working for.

Taylor said he texted Sondland, who asked him to call. "During that phone call, 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 U.S. election," Taylor wrote.

"Ambassador Sondland also told me that he now recognized that he had made a mistake by earlier telling the Ukrainian officials to whom he spoke that a White House meeting with President Zelinskiy was dependent on a public announcement of investigations — in fact, Ambassador Sondland said, 'everything' was dependent on such an announcement, including security assistance. He said that President Trump wanted President Zelenskiy 'in a public box' by making a public statement about ordering such an investigation."

5. Taylor says Trump officials denied a quid pro quo, while urging what appeared to be a quid pro quo

On September 7, the NSC official told Taylor about another disturbing conversation between Sondland and Trump.

"President Trump told Ambassador Sondlond that he was not asking for a 'quid pro quo.' But President Trump did insist that President Zelenskiy go to a microphone and say he is opening investigations of Biden and 2016 election interference, and President Zelenskiy should want to do this himself."

The next day, Taylor said he and Sondland spoke on the phone. According to Taylor, Sondland said he had told Zelenskiy and one of his top advisers "that, although this was not a quid pro quo, if President Zelenskiy did not 'clear things up in public,' we would be at a 'stalemate.'

"I understood a 'stalemate' to mean that Ukraine would not receive the much-needed military assistance. Ambassador Sondland said this conversation concluded with President Zelenskiy agreeing to make a public statement in an interview with CNN," Taylor wrote.

6. Taylor said Sondland told him it was just business as usual

Taylor said he objected to Trump's plans, telling Sondland it was "crazy" to hold up security assistance "for help with a political campaign."

The two spoke by phone on Sept. 8, and "Sondland 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 before signing the check."

Taylor said "the Ukrainians did not 'owe' President Trump anything, and holding up security assistance for domestic political gain was 'crazy.'"

The hold on the aid was lifted on Sept. 11.