US House Speaker Nancy Pelosi has announced that the House of Representatives is moving forward to draft articles of impeachment against President Donald Trump.

“Our democracy is what is at stake,” Ms Pelosi said. “The president leaves us no choice but to act.”

Ms Pelosi delivered the historic announcement as Democrats push toward a vote, possibly by Christmas.

With sombre tones, drawing on the Constitution and the Founding Fathers, Ms Pelosi stood at the speaker’s office at the Capitol and said she was authorising the drafting of formal charges “sadly but with confidence and humility”.

“The president’s actions have seriously violated the Constitution,” she said.

“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 jeopardising the integrity of our elections.

“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,” she said.

At the heart of the impeachment probe is a July call with the president of Ukraine, in which Mr Trump appeared to press the leader to investigate Democrats and political rival Joe Biden as Mr Trump was withholding military aid to the country.

Before Ms Pelosi made her statement, Mr Trump tweeted that if Democrats “are going to impeach me, do it now, fast”.

He said he wants to get on to a “fair trial” in the Senate. The president also said that Democrats have “gone crazy”.

At the White House, press secretary Stephanie Grisham tweeted that Ms Pelosi and the Democrats “should be ashamed”, then she, too, looked past the likely impeachment in the Democratic-controlled House to trial in the Republican-majority Senate.

Mr Trump later accused the “Do Nothing” Democrats of trying to impeach him over “two totally appropriate (perfect) phone calls with the Ukrainian President”.

“….This will mean that the beyond important and seldom used act of Impeachment will be used routinely to attack future Presidents. That is not what our Founders had in mind. The good thing is that the Republicans have NEVER been more united. We will win!” he added on Twitter.

The chairmen of the House committees conducting the impeachment inquiry will begin drafting the articles, and some politicians are expecting to remain in Washington over the weekend.

On Wednesday, Ms Pelosi met behind closed doors with her Democratic caucus, asking, “Are you ready?”

The answer was a resounding yes, according to those in the room.

Three leading legal scholars testified on Wednesday to the House Judiciary Committee that Mr Trump’s attempts to have Ukraine investigate Democratic rivals are grounds for impeachment.

A fourth expert called by Republicans warned against rushing the process, arguing this would be the shortest of impeachment proceedings, with the “thinnest” record of evidence in modern times.

Trump Impeachment
Nancy Pelosi announced that the House is moving forward to draft articles of impeachment against President Donald Trump (J Scott Applewhite/AP)

Mr Trump is alleged to have abused the power of his office by putting personal political gain over national security interests, engaging in bribery by withholding 400 million dollars in military aid Congress had approved for Ukraine, and then obstructing Congress by stonewalling the investigation.

Meanwhile, Mr Trump’s team fanned out across the Capitol with Vice President Mike Pence meeting with House Republicans and White House officials conferring with Senate Republicans to prepare for what could be the first presidential impeachment trial in a generation.

Mr Trump has lambasted the impeachment probe daily and proclaims his innocence of any wrongdoing, but he has declined to testify before House hearings or answer questions in writing.

Based on two months of investigation sparked by a still-anonymous government whistleblower’s complaint, the Intelligence Committee’s impeachment report released earlier this week found that Mr Trump “sought to undermine the integrity of the US presidential election process and endangered US national security”.

Republicans defended the president in a 123-page rebuttal claiming Mr Trump never intended to pressure Ukraine when he asked for investigations of Mr Biden and his son.