WASHINGTON - President Donald Trump became the third United States president in history to be impeached after the Democrat-controlled House of Representatives voted along party lines to formally charge him with abuse of power and obstruction of Congress over his conduct towards Ukraine.

The votes on Wednesday night (Dec 18) to charge the President with two articles of impeachment capped a highly partisan series of hearings and debates that will continue with a Senate trial to acquit him, or end his presidency by removing him from office.

The votes on the two articles of impeachment passed by 230 votes to 197 and 229 to 198. Underscoring the deep political divide in the US, all but two House Democrats voted for the first article of impeachment and all but three Democrats voted for the second, although Democratic presidential hopeful Tulsi Gabbard voted "present" on both articles instead of for them.

Mr Trump will be the first impeached president to seek re-election.

Only two other presidents have been impeached in the US' 243 years of history: Andrew Johnson in 1868 and Bill Clinton in 1998. Both were acquitted in the Senate, an outcome that is likely to be repeated this time round.

At a campaign rally in Battle Creek, Michigan - a state he narrowly won in 2016 - a defiant Mr Trump told supporters just after the House vote: "It doesn't really feel like we're being impeached... The country is doing better than ever before. We did nothing wrong."

"The Republican party has never been so affronted but they have never been so united as they are right now," he added.

White House press secretary Stephanie Grisham said in a statement that the President was confident he would be fully exonerated in the Republican-controlled Senate, which would "restore regular order, fairness, and due process, all of which were ignored in the House proceedings".

"Today marks the culmination in the House of one of the most shameful political episodes in the history of our nation. Without receiving a single Republican vote, and without providing any proof of wrongdoing, Democrats pushed illegitimate articles of impeachment against the President through the House of Representatives," she said in a statement.

Earlier, under the dome of the US Capitol, in an over six-hour debate steeped in history and historical significance, Democrats and Republicans invoked the nation's founding fathers, quoted the pledge of allegiance and drew parallels with previous impeachments and past wars as they took turns giving quick speeches that summed up their decision on whether to impeach.

"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," said House Speaker Nancy Pelosi as she opened the debate on Capitol Hill, as dozens of pro-Trump and pro-impeachment supporters protested outside.

House Intelligence chairman Adam Schiff made the Democratic case for impeachment, accusing Mr Trump of using his public office for personal political gain in pressuring Ukraine to announce an investigation damaging to Democratic front runner Joe Biden in July.

The first article of impeachment charges Mr Trump with abusing his office by suspending military aid and withholding a White House meeting until Ukraine announced an investigation.

"The President of the United States was willing to sacrifice our national security by withholding support for a critical strategic partner at war in order to improve his re-election prospects," said Mr Schiff. "He tried to cheat, and he got caught."

The second article of impeachment charges Mr Trump with obstructing Congress by instructing administration officials not to comply with subpoenas.

Republicans condemned the impeachment inquiry as a desperate witch hunt by a party with a vendetta against an undesired president, echoing Mr Trump's public letter to Ms Pelosi the previous day. They also said that due process had not been followed and the impeachment threshold of high crimes and misdemeanours had not been reached.

Said Republican Congressman Barry Loudermilk of Georgia: "When Jesus was falsely accused of treason, Pontius Pilate gave Jesus the opportunity to face his accusers. During that sham trial, Pontius Pilate afforded more rights to Jesus than the Democrats have afforded this President in this process."

Others decried the partisan nature of the impeachment process, including retiring centrist Will Hurd of Texas, who said that the House had not heard evidence beyond a reasonable doubt of bribery or extortion.

"Today, we have seen a rushed process divide our country," said Mr Hurd. "Today, a dangerous precedent will be set: Impeachment becoming a weaponised political tool."

With the President impeached, attention now turns to the Senate trial and how it should be conducted.

One option being discussed by Democrats - including Ms Pelosi - is to not send the articles of impeachment to the Senate, which is needed for an impeachment trial to begin, according to sources privy to thinking in the Democratic party.

At a press conference after the impeachment vote, the Speaker declined to commit to a timeline for doing so.

"So far, we haven't seen anything that looks fair to us," she said.