Donald Trump has become the third president in United States history to be impeached.

On Wednesday, the House of Representatives voted 230 to 197 in favour of charging the president over alleged abuse of power.

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The second article of impeachment, obstruction of Congress, was won 229 votes to 198.

It will now be up to the Senate in January to decide whether Trump is guilty as charged and should be removed from office.

The result of the second article of impeachment. Credit: CNN

The chances of a guilty verdict are highly unlikely, however, with a two-thirds majority needed to secure a conviction.

And the Republican-dominated Senate is almost certain to vote along party lines.

Protesters demonstrate as the House of Representatives debates on the articles of impeachment against President Donald Trump at the Capitol building on Wednesday. Credit: Matt Rourke / AP

The US president issued a flurry of tweets as the House of Representatives debated the move to impeach ahead of the two historic votes.

Opening the debate on Wednesday, house speaker Nancy Pelosi described Trump's actions as "tragic".

"We gather today under the dome of this temple of democracy to exercise one of the most solemn powers that this body can take, the impeachment of the President of the United States," she told the House.

House Speaker Nancy Pelosi speaks as the House of Representatives debates the articles of impeachment against President Donald Trump at the Capitol in Washington on Wednesday. Credit: house Television / AP

"If we do not act now we would be derelict in our duty.

"It is tragic that the President's reckless actions make impeachment necessary. He gave us no choice."

Trump responded by tweeting Pelosi would go down as the worst speaker in history, and went on to label the move to impeach "an assault on America".

All in capital letters. Followed by four exclamations marks.

On Tuesday, Trump sent a scathing letter to Pelosi, saying the Democrats were attempting an "illegal, partisan attempted coup".

"History will judge you harshly as you proceed with this impeachment charade," he said in the letter to Pelosi.

Two charges

The first article of impeachment alleges the US president asked Ukrainian President Volodymyr Zelensky to investigate a political rival, former Vice President Joe Biden (expected to be a Democrat contender in the 2020 presidential race) and his son, Hunter Biden.

Trump has accused Biden senior of using his position as vice president during the Obama presidency to help his son gain financial benefit from a Ukrainian energy company he was associated with.

President Donald Trump learnt of his fate while attending a rally in Michigan. Credit: Evan Vucci / AP

In the same phone call to the Ukrainian leader, there was evidence of a quid pro quo offer, the inquiry heard, with Trump suggesting $US400 million worth of military aid promised to the eastern European nation could be in jeopardy.

The second article of impeachment accuses Trump of obstructing Congress, by blocking testimony and refusing to provide documents in response to House subpoenas as the impeachment inquiry progressed.

No stain

As the debate progressed on Wednesday, White House counsellor Kellyanne Conway held a 40-minute press conference, telling the media Trump did not see impeachment as a "stain" on his legacy.

"We’re not fine with the impeachment, we think it's ridiculous," she said.

"But it’s preordained. It’s a conclusion in search of evidence."

The ongoing impeachment inquiry is enraging the president, who has responded with an escalating volley of indignant protestations on Twitter over recent days.

This is not withstanding the fact that Trump's almost inevitable exoneration in the Senate is likely to boost his chances of victory in the November 2020 election.

According to American broadcaster ABC, the Trump campaign claimed that in the 72 hours following Pelosi’s impeachment inquiry announcement, a drive for campaign funds on Facebook raised almost $AU22 million in small-dollar donations.

Two precedents

Only two presidents have been in impeached in US history - Andrew Johnson in 1868 and Bill Clinton in 1998.

Richard Nixon narrowly avoided impeachment over the Watergate scandal by resigning as US president in 1974.

Andrew Johnson, left, US president from 1865 to 1869, and Bill Clinton, president from 1993 to 2001. Credit: Getty

Clinton was impeached for lying under oath and obstructing justice during a sexual harassment lawsuit filed against him by Paula Jones.

The impeachment of Johnson, who filled the presidential vacancy following the assassination of Abraham Lincoln, took place in the aftermath of the American Civil War.

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Johnson was accused of attempting to remove the country's Secretary of War without the assent of Congress.

Both men went on to complete their presidential terms because the legislature failed to obtain the necessary two-thirds majority to secure a conviction.

Under the US constitution, presidents can be removed from office by Congress if a two-thirds majority in the Senate decides they have committed treason, engaged in bribery, or been found guilty of various other serious crimes or misdemeanours.