Two of Donald Trump’s top lieutenants were dragged further into the rapidly unfolding impeachment investigation on Monday – as Republicans distanced themselves from the president after he made a dark warning of a second US civil war.

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

“Our inquiry includes an investigation of credible allegations that you acted as an agent of the president in a scheme to advance his personal political interests by abusing the power of the Office of the President,” the committee chairmen said in a letter to Mr Giuliani.

Shortly afterwards, the Wall Street Journal 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.

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The political backlash marks the latest drama following the launch of the impeachment inquiry by House Democrats last week, sparked by the disclosure of a whistleblower report accusing the president of improperly using his office to pressure the Ukrainian government to launch an investigation into Mr Biden, his political rival.

The civil war uproar – which has included condemnation from Republicans as well as Democrats – offers yet another glimpse at the fracturing relationship between Mr Trump and those in his party, and came after Mr Trump highlighted a quote from a longtime evangelical pastor, Robert Jeffress, who was interviewed on Fox & Friends Weekend.

“If the Democrats are successful in removing the President from office (which they will never be), it will cause a Civil War like fracture in this Nation from which our Country will never heal,” Mr Trump tweeted on Sunday, adding a parenthetical to a quote from the Southern Baptist preacher.

The statement caused quite a stir, leading to several trending hashtags on Twitter – mostly from those mocking the idea that such a war would be sparked by the removal of a president accused of using his presidential powers to investigate a political rival.

But, others took that threat a bit more seriously, including Republican congressman Adam Kinzinger, who admonished the president for spreading a quote from a pastor known for attacking other faiths.

“I have visited nations ravaged by civil war. @realDonaldTrump I have never imagined such a quote to be repeated by a President,” Mr Kinzinger tweeted, tagging Mr Trump.

The decorated air force veteran who served in Iraq and Afghanistan as a pilot continued: “This is beyond repugnant.”

The comment was met with condemnation from others, especially Democrats, including Chris Murphy and Brian Schatz, who serve in the senate.

“He is going to keep talking like this, and some people are going to listen and do what he asks,” Mr Murphy, of Connecticut, tweeted.

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

It said that as with Mr Trump’s 25 July 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.

At the same time, the Washington Post said Mr Barr has sought the help of officials in Britain and Italy as he overseas several interrelated enquiries into the activities of the US intelligence community in 2016.

Justice spokeswoman Kerri Kupec said Mr Trump made the calls to foreign leaders on Mr Barr’s behalf.

The civil war comments came following a weekend in which Mr Trump and his allies fought back forcefully against the allegations from Democrats, and sought to frame the issue as one of Mr Biden’s corruption not the president’s.

For Mr Biden’s campaign, Mr Giuliani’s frequent TV appearances – in which he repeatedly claimed, without evidence, that Mr Biden’s son was potentially involved in criminal activity in Ukraine – were a problem in themselves.

Over the weekend, the campaign sent a letter to major networks in the US, and asked that the president’s personal attorney not be invited back onto their channels as a result of those unsubstantiated accusations.