The House of Representatives is pushing ahead with plans to impeach President Donald Trump, Speaker Nancy Pelosi has said.
The House was moving forward to draft articles of impeachment, a milestone moment and only the fourth time in US history that Congress has tried to remove a president.
''Our democracy is what is at stake," Ms Pelosi said.
"The president leaves us no choice but to act."
Ms Pelosi argued that "no one is above the law" and Mr Trump's actions were a "violation of the public trust and constitution".
At the heart of the battle is Mr Trump's request in July that Ukraine launch an investigation targeting former vice president Joe Biden, a front-runner to win the 2020 Democratic presidential nomination and a possible future rival for the White House.
Democrats say Mr Trump abused the power of his office by seeking personal political gain. He has denied any wrongdoing, saying there was no tit-for-tat with Ukraine and accusing the Democrats of a witch hunt.
Responding to the announcement, Mr Trump said his political rivals were trying to impeach him "over nothing".
"This will mean that the beyond important and seldom used act of Impeachment will be used routinely to attack future Presidents," he said.
He added: "The good thing is that the Republicans have NEVER been more united. We will win!"
It comes after he told Democrats earlier on Thursday that if they are going to impeach him "do it now, fast", saying he wants to expose "how corrupt our system is".
The president also said Democrats had "gone crazy".
White House press secretary Stephanie Grisham said the Democrats should be "ashamed" and argued the president had "done nothing but lead our country - resulting in a booming economy, more jobs and a stronger military".
The impeachment articles could be voted on over the next two weeks and if a simple majority of the House votes in favour, the president will be formally impeached.
If this happens, there will be a trial in the Senate to decide if he should be removed from office.
However, the Senate is controlled by Republicans and a two-thirds majority would need to vote in favour of convicting and removing the president.
The announcement came the day after the House Judiciary Committee held its first hearing in the inquiry, during which three of the four witnesses alleged Mr Trump had committed impeachable offences.
A fourth expert warned against rushing the process and said the impeachment proceedings had the "thinnest" record of evidence in modern times.
Ms Pelosi met behind closed doors with her Democratic caucus on Wednesday when she asked: "Are you ready?", the Associated Press news agency reported.
The answer was a resounding yes, people in the room told AP.
Democratic Rep Steve Cohen, who sits on the House Judiciary Committee, told CNN he believes the articles of impeachment will include the charges of abuse of power and obstruction of Congress.
The party has claimed Mr Trump used his position to solicit foreign interference to boost his chances of re-election next year.
In its impeachment report released earlier this week , Democrats say that not only did the president seek overseas help for his re-election campaign, but that he undermined national security in doing so.
The report said there was evidence that Mr Trump had conducted a "month's long effort" to "use the powers of his office to solicit foreign interference on his behalf in the 2020 election".
During Congress impeachment hearings, Mr Trump was accused of trying to put political pressure on Ukraine to dig up dirt on Mr Biden and his son.
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They say the president has made an "unprecedented" effort to obstruct the investigation after he refused to provide testimony from himself, or his advisers.
The president has vehemently denied any wrongdoing.
How likely is it that the president will be removed from office? - Cordelia Lynch, US correspondent
This is a historic milestone and a clear signal that Nancy Pelosi is confident she has the support the Democrats need to impeach Mr Trump.
The House Judiciary panel could now vote to recommend impeachment charges against Donald Trump to the House as early as next Thursday.
That means we could be looking at a vote on the House floor in the week beginning 16 December.
But the political dial hasn't shifted - Republicans and Democrats are as locked in their opposing lanes as voters are.
We saw a glimpse of that enmity when Nancy Pelosi sharply rebuked a reporter when he asked her if she hated the president.
She looked incredulous.
Some Republicans, though, truly believe the Democrats have been out to get Mr Trump from the start.
These proceedings will play out amid a profoundly partisan divide.
This is a Democratic initiative.
It seems all but certain Donald Trump will be impeached. That's quite a stain on your political record.
But not necessarily a disqualifying one.
The Republican Senate is highly unlikely to convict and remove him.
Mr Trump will relish them calling their own witnesses and making their case to the nation.
By February, he could be cleared and using impeachment as a rallying cry.
Democrats feel they are reluctantly duty bound to carry through with this, to protect national security and uphold the constitution.
But in this febrile climate, you're still left wondering if that lofty pursuit is one that still chimes with normal people in a highly disillusioned country.