US president Donald Trump was impeached by the House of Representatives in December 2019. Last week, the House sent the articles of impeachment to the Senate, which means the impeachment trial can begin.
Euronews takes a look at what we know so far and what's next.
How does the impeachment process work?
"Impeachment" is usually used in US politics to describe removal from office, but it actually only means to file formal charges. The House of Representatives votes to impeach, and the Senate then holds a trial and votes to decide whether to remove the official (president or otherwise) from office.
What does the US Constitution say about impeachment?
An American president can be impeached for treason, bribery, or other high crimes and misdemeanours, according to the US Constitution.
What's happened so far?
From September to November 2019, the House held the inquiry stage, and then hearings, of the impeachment process.
This led to the formal impeachment vote, held on December 18. The House voted to approve the charges of abuse of power against US president Donald Trump by 230 votes to 197 against.
On January 15, the House voted to send two articles of impeachment to the US Senate, and sent them the next day, which marked the start of the impeachment trial.
The House has also appointed seven "impeachment managers" from the Democratic party, who will argue the case that Trump must be removed from office during the Senate trial.
What happens now?
The Senate trial will start on Tuesday afternoon local time (January 21) and will run for several weeks, depending on how long each session runs. Hearings are planned to run every afternoon, Monday to Saturday, and are expected to last around two weeks.
Senate Majority Leader Mitch McConnell, will allot each side a total of 24 hours to present their arguments but the time must be confined to two working days, according to the text of his organizing resolution reported by NBC News.
Arguments will begin on Wednesday afternoon local time, setting up several long days.
What could happen in the trial?
The Senate would need two thirds of the vote, or 60 total votes out of 100, to remove Trump from office.
But a simple majority - 51 votes - is the benchmark needed to call witnesses to testify in the trial, and that may happen, because around four Republicans are expected to defect and vote to call for witnesses.
This would prolong the trial but an outcome in which the Senate convicts Trump and removes him from office would remain very unlikely.
Why is the Senate very unlikely to convict Trump?
It's very unlikely that the US Senate votes to convict Trump, because unlike the House of Representatives, which has a majority of Democrats, the Senate has a majority of Republicans, who will not vote to remove a Republican president.
What happens if Trump is convicted by the Senate?
This is extremely unlikely, but he would be removed from office and forbidden to hold federal office in the future.
Once removed from office, new charges could be brought against the former president.
Would Trump be the first president to be removed from office?
No US president has ever been pushed out of the White House this way, but Richard Nixon, who was president from 1969 until 1974, got close: he chose to resign before being removed from office.
So, yes: Trump could be the first president in US history to be removed by the Senate. But that's very unlikely - and so is the idea of Trump resigning.
Have others been impeached before?
Trump is the third president to go through the impeachment process. The House has impeached 19 people in the past, including many federal judges and two presidents: Andrew Johnson and Bill Clinton. Both were "saved" by the Senate, which voted not to convict them.
What happened in previous Senate trials?
In 1868, the Senate held the trial of president Andrew Johnson for 11 articles of impeachment, but failed to convict him as it fell short of the needed two-thirds majority by only one vote. After a recess, new votes led to the same one-vote short result. Johnson was not convicted.
In 1998, Clinton became the second president to be impeached by the House and his Senate trial began in January 1999. The Senate voted on two articles of impeachment and both failed to receive the necessary two-thirds majority. The first article received 45 votes in favour of conviction and 55 against; the second was 50-50. Clinton was not convicted.