A deeply divided Congress formally opened a new, public phase of its investigation into Donald Trump on Thursday as US politicians voted for the first time to advance the impeachment process targeting the US president.
"Today the House takes the next step forward as we establish the procedures for open hearings... so that the public can see the facts for themselves," House Speaker Nancy Pelosi said.
"What is at stake in all of this is nothing less than our democracy."
The House of Representatives voted along party lines, 232 to 196, to pass a resolution that lays out guidelines for the next stages of the impeachment process.
All Republicans opposed the measure, despite agitating for weeks for such a vote that could end the secretive depositions and bring the process into the open.
Rep. Doug Collins is joined by fellow Republican politicians. Source: AP
Democrats are seeking to learn whether Mr Trump abused his presidential power by pressuring a foreign government to investigate a domestic political rival.
Mr Trump has repeatedly branded the inquiry as illegitimate and politically motivated and he was true to form in his instant reaction to the vote in the bitterly divided House.
"The Greatest Witch Hunt In American History!" he boomed on Twitter.
White House press secretary Stephanie Grisham issued a longer statement, accusing opposition Democrats of being "fundamentally un-American" in their "unhinged obsession with this illegitimate impeachment."
"Democrats are choosing every day to waste time on a sham impeachment - a blatantly partisan attempt to destroy the President," she said.
House Speaker Nancy Pelosi as the House votes 232-196 to pass resolution on impeachment procedure to move forward. Source: AP
Mr Trump meanwhile called on Republicans to rally behind him even as he faced the embarrassing likelihood of becoming the third president in history to be impeached and placed on trial for removal in the Senate, over an alleged scheme to extort Ukraine's help to get him re-elected in 2020.
The embattled president retweeted a rallying cry from Fox News host Laura Ingraham that called on Republicans to "stand together and defend the leader of their party against these smears."
Mr Trump is accused of withholding military aid to compel Ukraine to mount a corruption probe against his Democratic election rival Joe Biden - effectively using US foreign policy in an illegal shakedown for his personal political benefit.
Mr Trump and loyal Republicans dismiss the case as a "sham," but congressional investigators have heard a steady flow of corroborating evidence from government officials testifying behind closed doors on Capitol Hill.
The landmark resolution did not have unanimous Democratic approval. Two Democrats joined all Republicans in opposing the measure, although former Republican Justin Amash, now an independent, supported it - and offered a searing warning to his former party.
"Excusing his misbehaviour will forever tarnish your name," he tweeted to Republicans. "History will not look kindly on disingenuous, frivolous, and false defences of this man."
The inquiry now moves into the public eye - giving Americans the chance to hear on live television the evidence against Mr Trump.
Rudy Giuliani (left) poses with US President Donald Trump. Source: AAP
The House Intelligence Committee, which has led the inquiry so far, will host open hearings, presenting witnesses and documentary evidence and allowing Republicans to challenge the case against the president.
The minority can also suggest subpoenas but majority Democrats have the final say, a rule that has angered Republicans.
"Trying to put a ribbon on a sham process doesn't make it any less of a sham," House Republican Jim Jordan fumed.
Democrats argue that the vote neutralises a key Republican talking point that the inquiry has no validity because the full House did not sign-on.
Neither the House rules nor the US Constitution requires such a vote to start an impeachment inquiry.
If the case against Mr Trump is deemed strong enough, the House Judiciary Committee will draw up formal charges against the president - articles of impeachment - to be voted on by the full House.
That process could be completed by year-end. The Democrat-controlled House is expected to approve impeachment, which would then see Trump go on trial in the Senate, where Republicans have a majority.
