Democrats in the United States (US) House of Representatives met on Saturday to prepare for what could be the final week of their months-old impeachment inquiry that has imperiled Donald Trump's presidency.

After emerging from an all-day closed door meeting, House Judiciary Committee Democratic lawmakers said they were still in the process of drafting formal charges, known as articles of impeachment, that the panel could recommend for a full House vote as early as Thursday.

Representative Jamie Raskin told reporters on Saturday evening the committee had spent the day digesting information they received from the House Intelligence Committee and constitutional law scholars who testified before Congress on Wednesday.

“So now we are in the process of putting the law and the facts together to begin to think about the next step,” he said.

The lawmakers released a 55-page report on Saturday morning outlining what they see as the constitutional grounds on which articles of impeachment could be built.

In releasing the report, the panel's Democratic chairman, Jerrold Nadler, said impeachment was the only way to hold the Republican president to account.

“President Trump abused his power, betrayed our national security, and corrupted our elections, all for personal gain,” Nadler said in a statement.

“The Constitution details only one remedy for this misconduct: impeachment.”

“Now we have the task of focusing on what the exact articles might be,” said Eric Swalwell, another Democratic lawmaker in the House Judiciary Committee, on his way out of Saturday's meeting.

The committee will hold a public hearing on Monday to consider evidence gathered in the inquiry.

Republicans have called for a full day of proceedings to examine their own evidence, including a 110-page report saying the inquiry had found no evidence of an impeachable offence.

On Friday, the White House told Nadler it would not take part in the panel's hearings and condemned the inquiry as “completely baseless.”

Nadler, in turn, expressed his disappointment: "The American people deserve answers from President Trump."

House Speaker Nancy Pelosi, the top Democrat in Congress, directed the committee to draw up the charges on Thursday after weeks of investigation into Trump's request that Ukraine investigate former vice president Joe Biden, a leading contender for the Democratic nomination to face the president in the 2020 US election.

Passage of formal charges in the Democratic-led House, now seen as all but certain, would lead to a trial in the Senate on whether to remove Trump from office. The Republicans who control the Senate have shown little sign of supporting Trump's removal.

While Trump has refused to cooperate with the House probe, he has made clear his lawyers will mount a defence in a Senate trial.

The Judiciary Committee is focused on two possible articles of impeachment that would accuse the president of abuse of power in his dealings with Ukraine and obstruction of Congress for refusing to cooperate with investigating committees.

Democrats also need to settle the question of whether to draft a third article alleging obstruction of justice based on former Special Counsel Robert Mueller's report on the federal investigation of Russian interference in the 2016 presidential election.

“That's something that we'll decide this weekend,” Representative Debbie Mucarsel-Powell told reporters on Friday.

The probe has focused on a July 25 telephone call in which Trump asked Ukrainian President Volodymyr Zelenskiy to open an investigation into Biden and his son Hunter, and into a discredited theory promoted by Trump and his allies that Ukraine, not Russia, meddled in the 2016 election.

Hunter Biden joined the board of Ukrainian energy company Burisma while his father was vice president. Trump has accused the Bidens of corruption. They have denied wrongdoing and the allegations have not been substantiated.

Trump's personal attorney, Rudy Giuliani, who traveled this week to Budapest and Kiev, said on Thursday that Americans would soon learn how Joe Biden had contributed to corruption in Ukraine.

“He's going to make a report, I think, to the attorney general and to Congress,” Trump told reporters at the White House on Saturday. “I hear he's found plenty.”

Democrats also have accused Trump of abusing his power by withholding $391 million in security aid to Ukraine — a vulnerable US ally facing Russian aggression — and holding back a coveted White House meeting with Zelenskiy as leverage to pressure Kiev into investigating the Bidens.

“A president who perverts his role as chief diplomat to serve private rather than public ends has unquestionably engaged in 'high crimes and misdemeanors' — especially if he invited, rather than opposed, foreign interference in our politics,” the Judiciary Committee Democrats said in their report on Saturday.

A finding of “high crimes and misdemeanors” would present a ground for impeachment under the constitution.

Republicans have said they want Hunter Biden and the anonymous whistleblower whose complaint sparked the impeachment inquiry to testify. Nadler, however, is considered unlikely to call them.

Trump is the fourth US president to face impeachment proceedings. None previous were removed from office, although Richard Nixon resigned as he faced almost certain impeachment in 1974 over the Watergate scandal.