A series of leading figures have said the scandal, which saw Mr Trump and his allies urge the Ukrainian authorities to re-open a dormant investigation into Mr Biden’s son Hunter, was so serious it demanded the ultimate sanction of impeachment.
Eric Swalwell, a Democratic congressman who previously ran for president and sits on the intelligence and judiciary committees, said a stranger had approached him at an airport to insist on Mr Trump’s impeachment.
“You all better get your act together and impeach him,” the man told him.
This echoes remarks by the chair of the House intelligence committee, Adam Schiff, who said the president’s conduct around the Biden-Ukraine affair that impeachment was “the only remedy that is coequal to the evil”.
Even Nancy Pelosi, the speaker of the House and leader of congressional Democrats, who has long downplayed the prospects of impeachment, said the scandal-rocked White House was set to enter a “grave new chapter of lawlessness which will take us into a whole new stage of investigation”.
The complex case revolves around Hunter Biden, who was appointed to the board of a Ukrainian gas company in 2014, while his father was vice-president and shortly after the revolution which overthrew the country’s pro-Russia government.
Two years later, Joe Biden led a drive by Western nations to get Ukraine to fire its chief prosecutor, who was seen as weak on corruption.
Mr Trump and his supporters have claimed for months the Bidens’ conduct was itself corrupt and the firing of the prosecutor an attempt to stop him investigating Hunter Biden’s gas company post.
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The president has now admitted he even used the Bidens as an example of the corruption Ukraine’s president Volodymyr Zelenskiy must root out, during a July phone call with the newly elected leader.
“It was largely the fact that we don’t want our people, like Vice President Biden and his son, creating to the corruption already in the Ukraine,” he told reporters.
Mr Biden has insisted there was nothing wrong with either his son joining the gas firm’s board or his actions over the fired prosecutor.
Earlier this year a leading Ukrainian official said there had been no wrongdoing by the Bidens, and the presidential candidate has now accused Mr Trump of an “overwhelming abuse of power” and called for an investigation.
“Trump’s doing this because he knows I’ll beat him like a drum,” he told reporters during a campaign stop in Iowa.
Trump describes whistleblower as “partisan.” A minute later, he says, “I don’t know the identity of the whistleblower.”
The latest chapter in the row between the White House and Democrats was sparked by the refusal of Mr Trump’s director of national intelligence to release a formal whistleblower complaint made by someone working for the United States’ intelligence agencies.
The person had made the report in August after becoming concerned Mr Trump’s July phone call had included “troubling” promises with a foreign leader, The Washington Post has reported.
The Wall Street Journal has reported Mr Trump asked eight times during the conversation for Mr Zelenskiy to open an investigation into the Bidens.
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In addition, Mr Trump’s pugnacious personal lawyer, Rudy Giuliani, has admitted he also asked for an anti-Biden probe to be launched during meetings with senior Ukrainian officials organised by the Trump administration.
Mr Schiff has issued a legal summons for the White House to hand over the substance of the complaint but has been rebuffed, sparking a constitutional tussle and growing calls for impeachment.
Mr Trump had “crossed the Rubicon” if the latest reports of his conduct were accurate, the senior Democrat said. Referring to Mr Giuliani, he added: “Betraying your country…is one thing when it’s done by the court jester, another thing when by the man who would be king.”