The revelation the Australian government broke with diplomatic protocol and allowed Mr Downer to be interviewed by the Federal Bureau of Investigation, during Democrat Barack Obama's final months as USA president, could damage Australia's relations with the man now in the White House.
The New York Times said top Australian officials broke diplomatic protocol to allow the agents to question the country's then-high commissioner to the United Kingdom a year ago, with the results - summarised and sent to Washington on August 2 - laying the foundations for what was then known by its code name, Crossfire Hurricane, and is now special counsel Robert Mueller's probe.
The breakthrough stemmed from a night of heavy drinking Mr Downer had with former Trump campaign aide George Papadopoulos at the Kensington Wine Rooms in London in May 2016.
On Thursday the New York Times reported that within hours of the FBI opening its investigation into the Trump campaign's ties to Russian Federation in the summer of 2016, it had flown two agents to London to meet Downer for a highly secretive interview, after Australian officials cleared the meeting.
The almost 2,000 pages of interviews do not appear to contain information that would change the course of Mueller's investigation into Trump's team and Russian Federation.
The Australian High Commissioner to The UK Alexander Downer
Trump has often spoken against the investigation, calling it a "witch hunt" and even suggesting there will be legal action taken against Mueller and his team.
Mr Papadopoulos became one of Mr Mueller's first scalps, pleading guilty to lying to officials.
The FBI codenamed their probe Crossfire Hurricane, a reference to lyrics in a Rolling Stones song.
In thousands of pages of interview transcripts with the participants of the June 2016 Trump Tower meeting shed new light on how eager Donald Trump Jr. and senior members of the Trump campaign were to obtain damaging information on Hillary Clinton - and how frustrated and angry they were that the material did not come to fruition.
Crossfire Hurricane began in August 2016, exactly 100 days before the November 8, 2016 presidential election won by Mr Trump and a month after the real estate mogul became the official Republican nominee.
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