Washington, DC – The Democrat-led US House of Representatives is set to reach a turning point in its inquiry into whether President Donald Trump improperly pressured the government of Ukraine to interfere in US politics, moving from an investigative phase to deciding whether Trump should be impeached.

With the president abroad at the NATO meetings in London, the shift marks a perilous moment in his troubled presidency after the release on Tuesday of a 300-page report by House Intelligence Committee investigators describing Trump’s months-long effort to pressure Ukraine.

The report issued by the House Intelligence Committee, together with the Foreign Affairs and Oversight committees, alleges Trump “subverted US foreign policy toward Ukraine” and “undermined” US national security by seeking two politically motivated investigations to “help his presidential re-election campaign”.

It also accuses Trump and his lawyers of obstructing the House impeachment investigation.

In a landmark hearing on Wednesday, four constitutional law scholars will discuss whether the case against Trump meets a political and legal test for impeachment.

“The big issue facing the Judiciary Committee is, what constitutes an impeachable offence,” said Melissa Murray, a professor of law at the New York University law school.

‘Stress test’

The US Constitution provides for the removal of a US president for commission of treason, bribery or “high crimes and misdemeanours”, a phrase that invokes politics as well as law, Murray told Al Jazeera.

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“What do these words mean? How have these words been interpreted? What did our founders mean by these words in the 1700s? The model was English common law and removal of a member of Parliament,” she said.

The four constitutional scholars testifying are Noah Feldman of Harvard Law School, Pamela Karlan of Stanford Law School, Michael Gerhardt, of the University of North Carolina School of Law and Jonathan Turley at George Washington University Law School.

Feldman has previously said Trump’s violation of informal democratic norms is a “stress test” for the constitution and that Trump’s pressure on Ukraine was an impeachable “abuse of power”. Turley leans towards Republicans’ narrative and has previously criticised the Democrat’s case as incomplete and short of “proof of an impeachable offence”.

“We have finished the investigative phase and now we are on to the charging phase where you take all the facts and present to a jury and ask what do we have here,” Barbara McQuade, a professor of law at the University of Michigan told Al Jazeera.

Republican allies of Trump issued a 123-page advance rebuttal of the Intelligence Committee report on Monday saying Democrats “have been working to impeach President Trump since his election” in an “orchestrated campaign to upend our political system”. The case against Trump is “based on the accusations and assumptions of unelected bureaucrats who disagreed with President Trump’s policy initiatives and processes”.

‘President’s political dirty work’

The Democrats’ investigation of Trump centres on a July 25 telephone call the president had with Ukrainian President Volodymyr Zelenskyy in which Trump asked for “a favour”.

Trump wanted Zelenskyy to open investigations into former Vice President Joe Biden and his son Hunter, who was a board member on the Ukrainian gas company Burisma, and into a debunked conspiracy theory that Ukraine, not Russia, hacked the US election in 2016.

At the time of the call, Trump was withholding $391m in critical US military and financial aid to Ukraine. His administration also conditioned a potential White House meeting with Zelenskyy on announcement of the investigations, witnesses told the Democrats’ impeachment inquiry last month.

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On the July 25 call, Trump asked Zelenskyy to talk to Rudy Giuliani, the president’s personal lawyer, who Trump had put in charge of policy towards Ukraine in May.

“This report chronicles a scheme by the president of the United States to coerce an ally, Ukraine, that is at war with an adversary, Russia, into doing the president’s political dirty work,” Representative Adam Schiff, the Democratic chairman of the Intelligence Committee, told reporters at the US Capitol on Tuesday.

“It involves a scheme in which Donald Trump withheld official acts, a White House meeting as well as hundreds of millions of dollars of needed military assistance in order to compel that power to deliver two investigations that he believed would assist his re-election campaign,” Schiff said.

Trump has denied any wrongdoing, labelling the probe a “witch-hunt”. The White House has also stonewalled the inquiry’s requests for testimony and documents.

One new element in the Intelligence Committee report released in draft form on Tuesday is telephone records obtained under subpoena from AT&T and Verizon, US telecommunications providers. The records show “considerable coordination” between Giuliani, the White House, former Ukrainian prosecutors, Victoria Toensing, a Trump-affiliated lobbyist, and Lev Parnas, a Giuliani associated who is facing charges in the US that he violated campaign finance laws, Schiff said.

Trump and Giuliani pose for photographs [File: Carolyn Kaster/AP Photo]

Schiff also said the committee was investigating whether Trump’s pressure on Ukraine goes back further than initially understood.

Three of the four experts on Wednesday “will make a powerful case that the definition of impeachable offences certainly encompasses what Trump is charged with doing,” said Laurence Tribe, a professor of law at Harvard who is advising Democrats on impeachment strategy.

“He is using the power of his office to manipulate foreign affairs. He is soliciting a bribe in the form of an illegal favour. This is the classic case of an impeachable offence,” Tribe told Al Jazeera.

Mitch McConnell, the No 1 Republican in the Senate, told reporters on Tuesday he is expecting the House to impeach Trump, triggering a Senate trial.

“It looks like we will get something,” McConnell said.

It would take 67 of 100 senators in the Senate to vote to remove the president from office. Republicans control the chamber 53-47.