The Democratic-led House Intelligence Committee subpoeanad Mr Trump’s lawyer Rudy Giuliani after he acknowledged on television that he asked the government of Ukraine to “target” former vice president Joe Biden.

The Wall Street Journal has also reported that secretary of state Mike Pompeo took part in the Trump-Zelensky phone call which triggered the push for impeachment.

A senior State Department official told the Journal that Mr Pompeo was among the administration officials who listened in on the call.

Meanwhile, Mr Trump’s promotion of an apparent threat of a second US civil war should Democrats remove him from office was met with consternation in Washington on Monday.

At the same time, it was reported Mr Trump pressed the prime minister of Australia to dig up information he hoped would discredit Robert Mueller’s Russia probe. The New York Times said the president had asked Scott Morrison to assist him in efforts to uncover how investigations of Russia began.

The report said that as with Mr Trump’s July 25 conversation with the leader of Ukraine, in which he asked him to dig up dirt on Mr Biden, an action that led Democrats to trigger impeachment probes, details of the president’s conversation with Mr Morrison were also kept in a particularly secure server.

The newspaper said officials had said Mr Trump asked Mr Morrison to help with an inquiry being pursued by attorney general William Barr, into how US investigative agencies began their probe of possible collusion between the Trump campaign and Russia over the 2016 election.

In doing this, Mr Barr has sought the help of the FBI and the National Security Agency. Mr Trump and others have claimed the the FBI began its probe into possible collision in late 2016, after being passed accusations made by former British MI6 agent Christopher Steele.

Yet, it has long been reported the FBI began its investigation into possible collusion after being tipped off by Australian diplomats in London that one of Mr Trump’s campaign advisors, George Papadopoulos, had been offering “dirt” on Mr Trump’s rival, Hillary Clinton.