Donald Trump's opponents say impeachment charges must come swiftly with 'democracy at stake'

The move has been derided by Donald Trump and other leading Republicans as a sham and a hoax.

However, Democrats have stated it is their duty, in the aftermath of the Ukraine probe. Republicans have repsonded by saying it will drive Ms Pelosi's majority from office.

Ms Pelosi, who urged Congress to act, said: "The democracy is what is at stake."

Mr Trump has insisted he did nothing wrong.

"The president's actions have seriously violated the Constitution," she said in a somber address at the Capitol. "He is trying to corrupt, once again, the election for his own benefit. The president has engaged in abuse of power, undermining our national security and jeopardizing the integrity of our elections."

Mr Trump has insisted he did nothing wrong. He tweeted that the Democrats "have gone crazy."

• READ MORE: Watch as Nato leaders appear to gossip about Donald Trump in unguarded chatAt the core of the impeachment probe is a July phone call with the president of Ukraine, in which Mr Trump pressed the leader to investigate Democrats, including political rival Joe Biden. At the same time the White House was withholding military aid from Ukraine, an ally bordering an aggressive Russia.

Drafting articles of impeachment is a milestone moment, only the fourth time in U.S. history Congress has tried to remove a president, and it intensifies the rigid and polarizing partisanship of the Trump era that is consuming Washington and dividing the nation.

The speaker delivered her historic announcement in solemn tones at the Capital, drawing on the Constitution and the Founding Fathers in forcefully claiming Congress' oversight of the president in the nation's system of checks and balances. Democrats are already beginning to prepare the formal charges, pushing toward House votes, possibly before Christmas.

• READ MORE: Alan Cumming warns Americans are being 'brainwashed' by Donald Trump"Sadly, but with confidence and humility, with allegiance to our founders and a heart full of love for America, today I am asking our chairmen to proceed with articles of impeachment," Pelosi said.

Seemingly eager to fight, Trump tweeted that if Democrats "are going to impeach me, do it now, fast." Though he has fought the House investigation, trying to bar current and former officials from testifying, he said he now wants to move on to a "fair trial" in the Senate.

Approval of articles of impeachment is considered likely in the Democratic-majority House. Conviction in a following trial in the Republican-dominated Senate seems very unlikely.

Ms Pelosi added she would have no regrets if impeachment ended up helping Trump's re-election effort. "This isn't about politics at all," she said. "It's about honoring our oath of office" - to defend the constitution.

Mr Trump's allies argue that voters, not lawmakers, should decide the president's future. But Democrats say the nation cannot wait for the 2020 election, alleging Trump's past efforts to have foreign countries intervene in the presidential campaign are forcing them to act to prevent him from doing it again.

Ms Pelosi said the still-anonymous whistleblower's complaint about Trump's Ukraine call changed the dynamic, creating the urgency to act.

Pulling from the House's 300-page investigation of the Ukraine matter, Democrats are focusing on at least three areas - abuse of power, bribery and obstruction - that could result in two to five articles, they say.

They argue that Trump abused the power of his office by putting personal political gain over national security interests; engaging in bribery by holding out $400 million in military aid that Congress had approved for Ukraine; and then obstructing Congress by stonewalling the investigation.