The US’s top diplomat in Ukraine, Bill Taylor, gave damning evidence on Tuesday to congressional committees in Washington investigating Donald Trump. Taylor told impeachment inquiry hearings that Trump had explicitly put pressure on Ukraine’s president, Volodymyr Zelenskiy, to investigate former vice-president Joe Biden – Trump’s Democratic rival in the 2020 election – and to pursue the conspiracy theory that Ukraine interfered in the 2016 US election on the side of Hillary Clinton. Taylor released his version of events in a 15-page document, in the most detailed account of the scandal so far.

Why did Taylor go to Ukraine?

Taylor, a veteran diplomat, said that in May he was offered the job of US ambassador to Ukraine. He had served as ambassador there before, between 2006-2009. Taylor said he had reservations about taking up the role because his predecessor, Marie Yovanovitch, had been “poorly treated” and caught up “in a web of political machinations both in Kyiv and Washington”. Taylor said he agreed on condition the US’s policy of strong military and political support for Ukraine continued, at a time when it was under Russian attack. The US secretary of state, Mike Pompeo, confirmed this. Taylor arrived in Kyiv in June. He took with him a letter from Trump inviting Ukraine’s new president Zelenskiy to the White House.

What did he find when he arrived?

Two foreign policies. In Kyiv, Taylor said he found a “confusing” and “ultimately alarming” situation. On the plus side, the new Zelenskiy government did appear to be making progress in tackling the country’s corruption. But Taylor said he discovered two distinct channels of “US policymaking”. One was regular. It included diplomatic support for reform. The other was “highly irregular” and run by some of Trump’s closest aides. They included special envoy Kurt Volker; the EU ambassador, Gordon Sondland; and the energy secretary, Rick Perry. Taylor said he later learned Trump’s personal lawyer Rudy Giuliani was involved. In late June Taylor said he “sensed something odd” about a planned call with Zelenskiy. Sondland told him that “regular interagency participants” would be excluded. And that he would pass on a demand from Trump to “get to the bottom of things”.

What did that mean?

Taylor said in mid-July it was clear that Trump wanted Zelenskiy to “investigate” two things. One was the conspiracy theory that Ukraine colluded with Hillary Clinton in 2016 to help her win the presidential election. The other was Burisma, the Ukrainian energy company where Hunter Biden – son of Joe Biden – had served on the board. The allegation, subsequently found to be untrue, was that Joe Biden had put pressure on the previous government of Petro Poroshenko to fire the prosecutor investigating Burisma, in order to help his son. Taylor said Giuliani was behind the “irregular policy channel” and that Trump would only meet with Zelenskiy if the Ukrainian president carried out these investigations. There was an explicit quid pro quo, Taylor suggested.

What happened next?

The White House put on hold almost $400m of military assistance promised to Ukraine. Taylor said he was astonished to learn of this, during a July conference call. The secretaries of defense and state, the CIA director and national security adviser all tried to get this overturned – without success. Taylor told Washington that Ukrainians in the east of the country would die without the assistance. Meanwhile, senior figures were furious that Trump was insisting on “investigations” before a meeting with Zelenskiy could take place. John Bolton called this “a drug deal” and told Fiona Hill, Trump’s senior Russia expert, to “brief the lawyers”. Taylor began keeping notes. Understandably, the Ukrainians were “confused” about US policy, he said.

Was there a phone call?

The notorious phone call between Trump and Zelenskiy took place on 25 July. Before the call, Sondland reportedly told Zelenskiy to tell Trump he would “leave no stone unturned” in investigating Biden. Taylor said he wasn’t given a readout of the conversation, which was “strange”. The ambassador became increasingly concerned by the lack of military aid to Ukraine. He asked Tim Morrison, Hill’s replacement on the National Security Council, about this and was told bluntly: “The president doesn’t want to provide any assistance at all.” Taylor said he wrote a cable to Pompeo setting out his concerns and saying it would be “folly” to deny the Ukrainians help when they were under attack.

What about CNN?

According to Taylor, Trump insisted that Zelenskiy make a public statement before he would meet with him. The Ukrainian president should appear on CNN and announce that he was opening an investigation into Biden and Ukraine’s 2016 election interference. Trump – according to Taylor – said that Zelenskiy had to “clear things up” and if he didn’t there would be “stalemate”. Taylor took that to mean no American weapons would be delivered. Zelenskiy was on the brink of caving in to Trump’s request but wanted the White House to announce a Trump-Zelenskiy meeting first. This sequence didn’t happen and so Zelenskiy didn’t appear on CNN, to Taylor’s great relief. The ambassador finally learned about the contents of the Zelenskiy-Trump phone call on 25 September, when the White House declassified it. The Ukrainians were “livid”, he said.