Donald Trump committed offences worse than Richard Nixon during Watergate and should be impeached for "high crimes and misdemeanors", constitutional scholars selected by Democrats told Congress yesterday.
However, another legal expert, selected by Republicans, said the impeachment case against Mr Trump was the "thinnest" ever, was "slipshod," and would create a "dangerous precedent" for future presidents.
The academics were called by the House judiciary committee, which is expected to draw up formal articles of impeachment against Mr Trump within days.
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Their role was to explain what the US Constitution’s framers intended impeachment to be for, and whether Mr Trump’s actions warranted it.
It came a day after the publication of a 300-page report by the Democrat-led House intelligence committee, based on public hearings, which found "serious misconduct" by the president, and evidence that was "overwhelming."
Mr Trump, speaking at the Nato summit in London dismissed the report as a "joke," and attacked Democrats for holding the latest hearing while he was abroad. "Do they, in fact, love our country?" he said.
The US president has been accused of pressuring Volodymyr Zelenskiy, the Ukrainian leader, to investigate Joe Biden, his potential Democrat rival in 2020, for corruption.
Mr Biden’s son Hunter was on the board of Burisma, a controversial Ukrainian energy company. The Bidens deny any wrongdoing.
Democrats claim that on July 25, in a call with Mr Zelenskiy, Mr Trump sought to leverage $391 million in US security aid to Ukraine to secure the Biden investigation. Mr Trump denies doing so.
Three scholars, called by Democrats on the judiciary committee, declared themselves "unanimous" that Mr Trump had abused his power and should be impeached.
In doing so they introduced references to historical figures including Louis XIV, Charles II, Sir Thomas More, and Alexander Hamilton.
Impeachment had been intended by the Constitution’s framers as a protection against monarchy, dictatorship, and corruption of elections, they said.
Michael Gerhardt, professor of constitutional law at the University of North Carolina, said Mr Trump’s actions were "worse than the misconduct of any prior president," including Richard Nixon during Watergate.
He said: "If Congress fails to impeach here, then the impeachment process has lost all meaning. And, along with that, our Constitution’s carefully crafted safeguards against the establishment of a king on American soil.
"This president has attacked each of the Constitution’s safeguards against establishing a monarchy in this country. If this is not impeachable then nothing is impeachable."
Prof Gerhardt added: "If left unchecked, the president will likely continue his pattern of soliciting foreign interference on his behalf in the next election."
He said Mr Trump had committed a litany of impeachable offences including bribery, abuse of power, obstruction of Congress, and obstruction of justice.
Noah Feldman, a Harvard law professor, added: "President Trump has committed impeachable high crimes and misdemeanors."
Pamela Karlan, a law professor at Stanford, said Mr Trump’s behaviour "struck at the very heart of what makes this country a republic."
However, Jonathan Turley, a law professor at George Washington University, the only witness called by Republicans, warned against impeachment.
He said Mr Trump’s phone call was "anything but perfect," and the president was not "right," but the case against him was "woefully inadequate and dangerous".
It had the "thinnest evidentiary record, and the narrowest grounds, ever used to impeach a president," and would "lower impeachment standards," he said.
Prof Turley told the Democrat-led committee: "I’m not a supporter of President Trump. I voted against him. I get it. You are mad. The president is mad. My Republican friends are mad. My wife is mad. My kids are mad. Even my dog is mad – and Luna is a golden doodle, and they are never mad.
"We are all mad, and where has it taken us? Will a slipshod impeachment make us less mad? Or, will it only give an invitation for the madness to follow in every future administration?"
He concluded: "It [impeachment of Mr Trump] is wrong. This is not how you impeach an American president."
Republicans in Congress have rallied around Mr Trump.
Doug Collins, the lead Republican on the judiciary committee, said: "This is not an impeachment. This is a simple railroad job. You [Democrats] just don’t like the guy. This partisan coup will go down in infamy in the history of the nation."