Will Donald Trump be impeached? Latest news from the inquiry, explained

Democrats have launched an impeachment inquiry into Donald Trump after accusing him of violating the US Constitution, plunging a deeply divided nation into yet another clash between Congress and the commander in chief.

The US president accused Democrats of another political "witch hunt", summing up his view of the probe in an all-caps tweet:

The Democrats' course of action has thrown up a number of questions - adding to the uncertainty already hanging over the 2020 election campaign - and tests anew the nation's constitutional system of checks and balances. We take a look at just a few of those questions below.

What is impeachment and has it happened before?

Impeachment is the process of removing a government official - in this case Donald Trump, the US president - from office. To trigger the process, an inquiry looks at whether the official's conduct falls under "treason, bribery, or other high crimes and misdemeanours”, as stated in Article Two of the US Constitution.

Where things get tricky is the Constitution does not define "high crimes and misdemeanours", so Congress must decide for itself what constitutes an impeachable offence. However, it is generally understood to mean a violation of an oath of office, rather than necessarily breaking the law.

Only three presidents have faced an impeachment inquiry - Andrew Johnson, Richard Nixon and Bill Clinton.

In 1868, Mr Johnson was impeached by the House on charges relating to violating the Tenure of Office Act, over his firing of his Secretary of War, but he was acquitted in the Senate. After the 1974 Watergate scandal, a House committee approved articles of impeachment against Mr Nixon, but he resigned before the full House held a vote. Mr Clinton was impeached by the House in 1998 on charges of perjury and obstruction of justice relating to a sexual harassment case against him but was then acquitted in the Senate.

No president has ever been formally removed by the Senate.

What is the Ukraine scandal at the heart of the inquiry?

At the heart of the issue is whether Mr Trump held back aid to Ukraine in a bid to pressure the country to investigate his political rival Joe Biden and his son Hunter. Mr Biden, the former US vice president, is currently the Democratic front-runner in the race to challenge Mr Trump for the White House in 2020.

The trigger for the impeachment investigation was a phone call between Mr Trump and the newly elected president of Ukraine, Volodymyr Zelenskiy. Concerns about the phone call were first revealed after a whistleblower filed a complaint accusing the president of abusing his power in order to interfere in the 2020 election.

The whistleblower, a CIA officer previously assigned to the White House, said several officials had raised concerns about Mr Trump's conversation with Mr Zelenskiy. In response, the House Speaker Nancy Pelosi announced in late September that the chamber would open a formal impeachment proceeding to investigate the claims.

A day after the impeachment investigation began, the White House released a redacted version of the phone call which revealed that Mr Trump had indeed urged Mr Zelenskiy to do him a "favour" and investigate the Bidens.

Overshadowing the request was the fact that it came days after Mr Trump held back almost $400 million in military aid that Congress had approved for Ukraine to defend itself against Russia. Mr Trump has insisted he did nothing wrong in calling for the investigation, saying there was no "quid pro quo" in his dealings with Ukraine.

Why was Mr Trump calling for an investigation into the Bidens?

Mr Trump and his allies have repeatedly suggested that while he was vice president, Mr Biden pushed for Ukraine's then prosecutor general, Viktor Shokin, to be fired because he had been investigating Burisma, a Ukrainian gas company where his son Hunter held a lucrative board position.

The Bidens have vehemently denied any wrongdoing and in fact Mr Biden was not alone in calling for Mr Shokin's removal. The US government was backed by several European allies and the International Monetary Fund in criticising Mr Shokin for failing to tackle corruption, including in his own office.

Mr Trump and others have also repeated an unfounded conspiracy theory that Ukraine is in possession of a server containing hacked Democratic Party emails.

Since the impeachment investigation began, several key witnesses have given evidence revealing they had raised concerns about a shadow foreign policy being waged through Mr Trump's personal lawyer, Rudy Giuliani, to advance the president's own political agenda. One threat for the investigators is whether they lobbied for the removal of the US ambassador to Ukraine by pushing allegations she was against Mr Trump.

Among the most damning testimony was that of William Taylor, the acting ambassador to Ukraine, who told Congress that Mr Trump had made the release of military aid conditional on Ukraine opening an investigation into the Bidens. The House committees have also released a string of text messages between Mr Taylor and other administration officials, in which Mr Taylor writes: "I think it’s crazy to withhold security assistance for help with a political campaign”.

How does the impeachment process work?

Any House committee can bring charges of impeachment. Currently, there are six ongoing investigations into Mr Trump. Adam Schiff, chair of the House Intelligence Committee, has taken the most prominent role in leading the investigation so far, working with around three other committees.

Over the next few months, six committees in the Democrat-controlled House will pursue an investigation that is likely to result in the chamber bringing articles of impeachment against Mr Trump. The investigators are also seeking evidence from several members of Mr Trump's inner circle, including Mr Giuliani, Mike Pompeo, the US secretary of state, and former national security adviser John Bolton.

The White House has refused to co-operate with the probe, calling it a "sham", but several current and former officials have already defied that edict to appear before investigators. House Republicans have also criticised the process and stormed one of the secure rooms where depositions are being held to publicise their opposition to the closed-door hearings.

On October 31, the House held its first formal voted on its bid to oust Mr Trump, moving to progress the impeachment investigation into a public phase. The vote was 232 to 196 in favour of a resolution that outlined how the impeachment inquiry will progress. It means that investigators will soon hold hearings in the open and give both Republican and Democrat members the chance to question the witnesses called to give testimony. However leading House Republican dismissed the vote, calling it a "tainted process".

If the investigation concludes there is a cause for impeachment, the House Judiciary Committee will draw up articles of impeachment and vote on them.

It will then go to a House-wide vote which requires a simple majority to pass. If the vote passes, Mr Trump will have been impeached - but not removed from office.

A trial is then held in the Senate, with the House appointing members to act as 'prosecutors' and all 100 senators acting as 'jurors'. The chief justice of the Supreme Court oversees the trial. Two thirds of the Senate must find Mr Trump guilty in order for him to be convicted and removed from office. In such an event, the vice president becomes president.

What does the country think about impeaching Trump?

For Mr Trump's first two years in office, the majority of the American public appeared to be against impeachment. That appears to have changed in the wake of the Ukraine scandal.

Since the impeachment inquiry began, multiple polls, including one by the conservative network Fox News, have showed more of the public now favour an impeachment inquiry than oppose it. But it is a slim margin and there is a danger for Democrats that if the investigation drags on too long and becomes too complex, public mood will shift again.

There were initial suggestions a House vote to impeach Mr Trump could happen as early as the end of November - but it could stretch into the new year. That could also cause an issue for Democratic presidential candidates, who do not want the issue hanging over an election year.

So will Trump really be impeached and removed?

In short, it seems pretty unlikely Mr Trump will be booted out of the White House. While Mr Trump is likely to be impeached by the House, where Democrats enjoy a majority, he is unlikely to be convicted by the Senate.

The Republican Party holds a 53-47 majority in the Senate, which means around 20 senators would have to turn on their own president and vote against him. It would take something major for that to happen.

Mr Trump's approval rating among his base remains strong and Republican voters are overwhelmingly against impeachment so senators are wary of going against his supporters, particularly with the election just a year away.

There are some cracks in the Republican flank. Senior figures like senator Mitt Romney called the incident "deeply troubling" and former Ohio governor John Kasich said it made him "sick to my stomach".

But by and large Republicans in the House and the Senate have remained tight lipped -  acutely aware that voters in their home districts remain loyal to the president.

The handful of sitting Republicans who have openly criticised Mr Trump's actions are typically from states where the president doesn't enjoy strong support.

Which Republican senators could turn?

No Republican senator has publicly said they will back Mr Trump's removal, but suspicion has fallen under a number of names based on comments they have made since the scandal broke.

Mitt Romney

Mitt Romney is one of Mr Trump's most vocal critics within the Republican Party. He represents Utah, a state where the president is not popular, and does not face re-election until 2024, which gives him a licence to speak his mind on impeachment. He has refused to rule out impeaching the president, Mr Trump's actions on Ukraine "wrong and appalling".

Cory Gardner

Cory Gardner faces a tough re-election battle in Colorado, a swing state. Mr Gardner has publicly called Mr Trump's phone call with the Ukrainian president a “serious issue”. Asked if he still supported Mr Trump’s reelection, Mr Gardner refused to say, adding: “Let’s find out what’s happening. Let’s get to the bottom of this.”

Lisa Murkowski

Lisa Murkowski, a senator for Alaska, publicly broke with the White House position on the Ukraine scandal, saying: “You don’t hold up foreign aid that we had previously appropriated for a political initiative. Period.”

Ben Sasse

The senator for Nebraska recently broke his silence on the Ukraine scandal, saying: “American elections should be for Americans. And the idea that we would have foreign nation-states coming into the American electoral process, or the information surrounding an election, is really, really bad.” However he later added: “Republicans ought not just circle the wagons, ... and Democrats ought not have been using words like impeachment before they knew anything about the actual substance.”

Martha McSally

Martha McSally is thought to be one of the most endangered Republicans in the Senate with Democrats hopeful they can take her Arizona seat in 2020. She criticised what she termed "partisan bickering" in the House impeachment investigation but also said it was a "serious matter". Ms McSally has dodged questions about whether Mr Trump's Ukraine call was acceptable, but said: "If it comes to the Senate, I'm actually a juror ... so my job is to be thoughtful, to look at the facts and to show good judgment."