The impeachment investigation into Donald Trump has entered a new phase as the House Judiciary Committee begins hearings into Mr Trump's conduct.
The public testimony by four experts on constitutional law comes one day after the House Intelligence Committee laid out the case for removing Mr Trump.
The intelligence panel's report said evidence of Mr Trump's misconduct was "overwhelming".
If impeachment passes in the House, the US Senate will put Mr Trump on trial.
The impeachment process began in September after an anonymous whistleblower complained to Congress about a July phone call by Mr Trump to the president of Ukraine, in which Mr Trump appeared to tie US military assistance to Ukraine launching investigations which would help him politically.
The White House has denied allegations made by Democrats – that Mr Trump put his own personal political interests "above the national interests of the United States" by soliciting foreign interference in the 2020 US elections, as the 300-page report argues.
After the report's release on Tuesday, White House spokeswoman Stephanie Grisham said that it "utterly failed to produce any evidence of wrongdoing".
Speaking from the UK, where he is attending a Nato summit, Mr Trump questioned the patriotism of Democrats. "You almost question whether or not they love our country and that's a very serious thing: Do they love our country?" he said on Wednesday.
Among formal impeachment charges expected to be considered by the judiciary committee are abuse of power, obstruction of justice and contempt of Congress.
Democrats are keen to hold a vote on impeachment in the House of Representatives before the end of the year, with the prospect of a trial in the Senate perhaps as early as January 2020.
What is the judiciary committee's role?
The judiciary committee has the power to formally draft articles of impeachment and submit them for a full vote in the House of Representatives.
The committee is hearing on Wednesday from four law professors – three picked by Democrats and one by Republicans.
Chosen by the Democrats are Stanford University's Pamela Karlan, Harvard University's Professor Noah Feldman and from the University of North Carolina, Michael Gerhardt.
George Washington University's Jonathan Turley was picked by Republicans.
The lawyers will interpret the impeachment clause of the constitution, which allows for presidents to be removed from office due to "high crimes and misdemeanours".
The White House was invited to participate in the hearing, but on Sunday declared that they would not send any administration officials to attend. Mr Trump was scheduled to return from London to Washington later on Wednesday, after the first judiciary hearing has concluded.
But on Wednesday, Mr Trump announced that he would depart early, skipping a final news conference "because we did so many over the past two days". His hasty departure came soon after a video emerged of other world leaders at the Nato conference appearing to mock him.
What has Trump said about the experts?
"They get three constitutional lawyers… and we get one," Mr Trump said on Tuesday during a bilateral meeting with Canadian Prime Minister Justin Trudeau in London. "That's not sounding too good, and that's the way it is.
"It's all nonsense, just wasting their time, and we get one. Ok. Nobody needs to know anything about constitutional law," he said.
What will the experts say?
The opening statements of the four witnesses has already emerged in US media.
Prof Feldman will say that the "evidence clearly constitutes" an impeachable offence because Mr Trump's interactions with Ukraine show him "corruptly using the powers of the presidency for personal political gain".
Prof Karlan will say Mr Trump "must be held to account" for "violating his oath to 'faithfully execute' the laws and to 'protect and defend the constitution'".
Mr Trump has attacked the "safeguards against establishing a monarchy in this country", Prof Gerhardt states.
"The president's serious misconduct, including bribery, soliciting a personal favour from a foreign leader in exchange for his exercise of power, and obstructing justice and Congress are worse than the misconduct of any prior president, including what previous presidents who faced impeachment have done or been accused of doing," he will say, according to his opening remarks.
Prof Turley, who was chosen by Republicans, will say "this is not how an American president should be impeached" and will warn that Democrats are setting a dangerous precedent.
"I get it. You are mad. The President is madRead More – Source