From Giuliani’s perspective, those who criticise him are “morons” and he “will be the hero” in this episode, he told The Atlantic magazine.

Giuliani was once called America’s Mayor, the man whose moxie and grace in the death and rubble of September 11 personified his stricken city and won him admiration around a shocked world.

Now he blends a sentiment that was familiar from that time and is familiar again in the world view of Trump himself: You’re with us or against us. If you’re not with me, you’re the enemy – of the president, the people, the country.

Citing the accounts of mostly unidentified US officials, and buttressed by Giuliani’s own words from countless turns on Fox News, his tweets and newspaper interviews, the anonymous whistle-blower pieced together a systematic effort by Giuliani on behalf of Trump to get Ukraine to investigate Biden and his businessman son, Hunter.

Trump made that appeal explicitly in a July phone call that is at the heart of the whistle-blower’s complaint. “I would like for you to do us a favour,” Trump said.

But the whistle-blower goes well beyond the phone call to lay out Giuliani’s efforts back to late last year. He traces the consternation that Giuliani’s machinations were causing inside the US administration and even among some people in the White House itself.

“Starting in mid-May, I heard from multiple US officials that they were deeply concerned by what they viewed as Mr Giuliani’s circumvention of national security decision-making processes to engage with Ukrainian officials and relay messages back and forth between Kiev and the president,” says the whistle-blower.

White House tried to cover up Trump’s Ukraine report, whistle-blower alleges

“These officials also told me that State Department officials, including Ambassadors Volker and Sondland, had spoken with Mr Giuliani in an attempt to ‘contain the damage’ to US national security,” the whistle-blower continues.

Kurt Volker, official US envoy for Ukraine negotiations, and Gordon Sondland, US ambassador to the European Union, also met officials from the new Ukrainian administration and “sought to help Ukrainian leaders understand and respond to the differing messages they were receiving from official US channels on the one hand, and from Mr Giuliani on the other”.

The complaint cites published reports of meetings Giuliani held with Ukraine’s chief prosecutor in New York in January and Warsaw, Poland, in February, after a phone call he had late in 2018 with the prosecutor’s predecessor. Giuliani associates later travelled to Kiev and met the chief of the security service and another close adviser to Zelensky, the complaint states.

This was the month Giuliani himself planned to go, and he was blunt to The New York Times about his purpose when his intended trip came to light. He intended to press for an investigation that would be helpful to Trump’s re-election.

“We’re meddling in an investigation, which we have a right to do,” he said. “There’s nothing illegal about it,” though “somebody could say it’s improper”.

The next day, he cancelled the trip and complained about the lack of cooperation from the new Ukrainian administration. Zelensky is “surrounded by enemies of the [US] president”, he said, “and of the United States”.

In this period, the whistle-blower says, citing the “general understanding” of US officials close to the matter, the Ukrainian leadership was led to believe that the prospects for a meeting or phone call between Trump and Zelensky would depend on whether the Ukrainian president “showed willingness to play ball”.

In June, Giuliani tweeted his frustration about Zelensky's “silence” on the matters he wanted him to pursue.

Then in July, says the whistle-blower, “I learned of a sudden change of policy with respect to US assistance for Ukraine” – namely that Trump had personally instructed all US agencies to suspend all military aid to Ukraine.

A week later, Trump and Zelensky had their July 25 phone call.

‘I’ve made him more famous’: Trump’s bizarre meeting with Ukraine’s leader

The complaint states that about a week after the call, Giuliani travelled to Madrid, Spain, to follow up with a Zelensky aide about matters arising from the phone call.

And about a week after that, Trump took a conciliatory tone, calling Zelensky a “very reasonable guy” and dangling the possibility of a White House visit for him. The two met this week at the United Nations. The military aid that had been held up was eventually released. There’s no sign that the Bidens are under any official Ukrainian investigation for Hunter Biden’s business relationships in that country when his father was vice-president.

To the whistle-blower, the episode shows Trump “using the power of his office to solicit interference from a foreign country in the 2020 US election”, with Giuliani “a central figure in this effort”.

During the special counsel’s Russia probe, Giuliani proved more useful for commanding headlines than in the courtroom. He became a staple on cable news, the face of a legal team that helped Trump emerge from the investigation with a less damaging result than many had expected.

Now Giuliani is doing some damage-control for himself, as some Republicans suggest Trump was ill-served by his interventions.

“It is impossible that the whistle-blower is a hero and I’m not,” he told The Atlantic. “And I will be the hero! These morons – when this is over, I will be the hero.”