WASHINGTON (AP) - House Democrats are poised to unveil two articles of impeachment against President Donald Trump - abuse of power and obstruction of Congress - with an announcement expected early on Tuesday (Dec 10).

Democratic leaders are pushing ahead with formal charges saying the President put US elections and national security at risk by asking Ukraine to investigate his rivals, including Mr Joe Biden, while withholding military aid for an ally trying to counter hostile Russia neighbours. They warn Mr Trump could do it again if left unchecked.

Speaker Nancy Pelosi declined during an evening event on Monday to discuss the articles or the coming announcement.

Details were shared by multiple people familiar with the discussions but unauthorised to discuss them and granted anonymity.

When asked if she has enough votes to impeach the President, the Democratic leader said she would let House lawmakers vote their conscience.

"On an issue like this, we don't count the votes. People will just make their voices known on it," Ms Pelosi said at The Wall Street Journal CEO Council.

"I haven't counted votes, nor will I."

The outcome, though, appears increasingly set as the House prepares to vote, as it has only three times in history against a US president.

Mr Trump spent part of the day tweeting against the impeachment proceedings, but did not immediately respond late on Monday.

The President and his allies have railed against the "absurd" proceedings, with Republicans defending the President as having done nothing wrong ahead of the 2020 election.

Ms Pelosi convened a meeting of the impeachment committee chairmen at her office in the Capitol late on Monday following an acrimonious, nearly 10-hour hearing at the Judiciary Committee, which could vote as soon as this week.

"I think there's a lot of agreement," Representative Eliot Engel of New York, the Democratic chairman of the Foreign Affairs committee, told reporters as he exited Ms Pelosi's office.

He said there would be an announcement in the morning.

"A lot of us believe that what happened with Ukraine especially is not something we can just close our eyes to," Mr Engel said.

At the hearing, Democrats said Mr Trump's push to have Ukraine investigate rival Joe Biden while withholding US military aid ran counter to US policy and benefited Russia as well as himself.

"President Trump's persistent and continuing effort to coerce a foreign country to help him cheat to win an election is a clear and present danger to our free and fair elections and to our national security," said Mr Dan Goldman, the director of investigations at the House Intelligence Committee, presenting the finding of the panels' 300-page report of the inquiry.

Republicans rejected not just Mr Goldman's conclusion of the Ukraine matter; they also questioned his very appearance before the Judiciary panel.

In a series of heated exchanges, they said Representative Adam Schiff, the chairman of the Intelligence Committee, should appear rather than send his lawyer.

"Where's Adam?" thundered Representative Doug Collins of Georgia, the top Republican on the Judiciary Committee.

"We want Schiff," echoed Trump ally Representative Matt Gaetz, a Florida Republican.

From the White House, Mr Trump tweeted repeatedly, assailing the "Witch Hunt!" and "Do Nothing Democrats".

The hearing set off a pivotal week as Democrats march towards a full House vote expected by Christmas.

In drafting the articles of impeachment, Ms Pelosi is facing a legal and political challenge of balancing the views of her majority while hitting the Constitution's bar of "treason, bribery or other high crimes and misdemeanours".

Some liberal lawmakers wanted more expansive charges encompassing the findings from former special counsel Robert Mueller's probe of Russian interference in the 2016 election.

Centrist Democrats preferred to keep the impeachment articles more focused on Mr Trump's actions towards Ukraine.

Representative Jerrold Nadler, a New York Democrat, was blunt as he opened Monday's hearing, saying: "President Trump put himself before country."

Mr Trump's conduct, Mr Nadler said at the end of the day-long hearing, "is clearly impeachable".

Mr Collins said Democrats are racing to jam impeachment through on a "clock and a calendar" ahead of the 2020 presidential election.

"They can't get over the fact that Donald Trump is the President of the United States, and they don't have a candidate that can beat him," Mr Collins said.

In one testy exchange, Republican attorney Stephen Castor dismissed the transcript of Mr Trump's crucial call with Ukraine as "eight ambiguous lines "that did not amount to the President seeking a personal political favour".

Democrats argued vigorously that Mr Trump's meaning could not have been clearer in seeking political dirt on Mr Biden, his possible opponent in the 2020 election.

Republicans also revived criticism of Mr Schiff's decision to expose phone records of members of Congress.

The inquiry showed that Mr Trump's personal lawyer Rudy Giuliani was in frequent contact with California Representative Devin Nunes, the top Republican on the House Intelligence Committee.

Mr Collins accused Democrats of engaging in a "smear" campaign against lawmakers by disclosing phone records.

But Mr Goldman said investigators did not subpoena lawmaker accounts but simply matched them up once they appeared in the records.

The Republicans tried numerous times to halt or slow the proceedings, and the hearing was briefly interrupted early on by a protester shouting, "We voted for Donald Trump!"

The protester was escorted from the House hearing room by Capitol Police.

The White House is refusing to participate in the impeachment process, and Mr Trump appears to be focused elsewhere - on Mr Giuliani's own probe and the President's upcoming campaign rallies.

Mr Trump and and his allies acknowledge he likely will be impeached in the Democratic-controlled House, but they also expect acquittal next year in the Senate, where Republicans have the majority.

The President was focused instead on Monday's long-awaited release of the Justice Department report into the 2016 Russia investigation.

The inspector-general found that the FBI was justified in opening its investigation into ties between the Trump presidential campaign and Russia and that the FBI did not act with political bias, despite "serious performance failures" up the bureau's chain of command.

Those findings undercut Mr Trump's claim that he was the target of a "witch hunt", rejecting theories and criticism spread by Mr Trump and his supporters.

Yet it found errors and misjudgments likely to be exploited by Republican allies as the President faces probable impeachment.

As the House pushes ahead toward votes, Mr Giuliani said on Monday he'll soon be releasing findings from his own recent visit to Ukraine.

Democrats say Mr Trump abused his power in a July 25 phone call when he asked Ukrainian President Volodymyr Zelensky for a favour in investigating Democrats.

That was bribery, they say, since Mr Trump was withholding nearly US$400 million (S$543.95 million) in military aid that Ukraine depended on to counter Russian aggression.

Ms Pelosi and Democrats point to what they call a pattern of misconduct by Mr Trump in seeking foreign interference in elections from Mr Mueller's inquiry of the Russia probe to Ukraine.

In his report, Mr Mueller said he could not determine that Mr Trump's campaign conspired or coordinated with Russia in the 2016 election.

But Mr Mueller said he could not exonerate Mr Trump of obstructing justice in the probe and left it for Congress to determine.