Donald Trump will face the most dramatic episode of his turbulent presidency on Tuesday when the Senate opens what will be only the third impeachment trial of a US president since the founding of the republic.
Mr Trump will be removed from office if convicted. But that outcome is extremely unlikely given that 20 Republican senators would have to support his conviction, and none of the 53 Republican senators have suggested that they would vote in that direction.
The Democratic-controlled House of Representatives impeached Mr Trump in December for abusing his office and obstructing Congress. Now the action moves to the Senate, where the trial of the 45th US president will take place.
The move came months after a CIA whistleblower raised concerns about a July 25 phone call in which Mr Trump pressured the Ukrainian president to dig up dirt on former vice-president Joe Biden, Mr Trump’s main Democratic rival in the 2020 election.
Mr Trump has argued that the call was “perfect”. But a parade of former and current officials provided Congress with dramatic public testimony laid bare a “quid pro quo” that involved Mr Trump withholding military aid to Ukraine to pressure Kyiv.
Here is the Financial Times guide to the trial:
How will the trial proceed?
John Roberts, the Supreme Court chief justice who will preside over the trial, on Thursday swore in the senators who will be jurors, paving the way for the trial to start on Tuesday. It will run six days a week and is expected to continue for several weeks.
The 53 Republican and 47 Democratic senators are not allowed to talk during the trial and must surrender their phones and other electronic devices. After reviewing the evidence, they will vote on whether to convict Mr Trump, and thus remove him from office. Mr Trump is the third president to face an impeachment trial after Bill Clinton and Andrew Johnson, who were acquitted.
How will the rules for the trial be determined?
The constitution provides little guidance on the rules. Mitch McConnell, the top Senate Republican, says he has crafted a package of rules to guide the trial, but has provided few details. The Democrats will have almost no influence on the rules unless they can persuade four Republicans to vote with them, which might be achievable.
What happens after the rules are set?
The senators will hear the case for the prosecution made by seven Democratic “impeachment managers” led by Adam Schiff, head of the House intelligence committee. They will also hear the case for the defence from Pat Cipollone, White House counsel, as well as high-profile lawyers Kenneth Starr, the independent counsel who tried to unseat Mr Clinton, and Alan Dershowitz, the Harvard law professor. After they have heard the opening arguments from both sides, they can then submit questions in writing.
In the next stage, the Democrats will almost certainly make a motion to call witnesses. They are particularly interested in hearing from John Bolton, the former national security adviser, and Mick Mulvaney, the acting White House chief of staff.
Will the Republicans allow the Democrats to call witnesses?
Mr McConnell does not want witnesses to avoid further tarnishing his party. But several Republicans who are facing tight re-election races this year will have to make a difficult decision: how to position themselves between the pro-Trump conservative base and independents who want Mr Trump to face tougher scrutiny.
If the Democrats are successful, Mr Trump may call his own witnesses. Some Republicans want him to call Mr Biden and his son Hunter, in an effort to prove a debunked conspiracy theory that they were engaged in Ukraine-related corruption.
The Republicans who may vote to call witnesses
The one-time presidential candidate was elected US senator from Utah in 2018, and will not face re-election for another four years. A critic of Mr Trump, Mr Romney has backed Mr McConnell’s handling of the impeachment but said he was “open” to hearing from witnesses, particularly Mr Bolton.
The senior senator from Maine, who has been in the Senate for more than two decades and is frequently among a handful of Republicans who vote against the party leadership, is up for re-election this year. She told the Bangor Daily News, a newspaper in Maine, that she was working with a “fairly small group” of Republicans to ensure witnesses will be called.
The senior senator from Alaska was re-elected in 2016 with 44 per cent of the vote. While Ms Murkowski said just before Christmas that she was “disturbed” by Mr McConnell’s co-ordination with the White House ahead of the impeachment trial, she has supported the majority leader’s plan to vote on whether to call witnesses after the trial is under way.
The junior senator from Colorado is seen as the most vulnerable Republican seeking re-election this year, having won his Senate seat in 2014 by only 2 percentage points. Mr Gardner has expressed concerns about the impeachment probe — telling the Denver Post that it has been a “total circus that has only served to divide the country” — but has yet to state his position on calling more witnesses.
The senior senator from Tennessee is seen as a close ally of Mr McConnell. But he is also retiring at the end of this year, and has been described as an “institutionalist” who is likely to support the calling of witnesses. He has told reporters that he might vote in favour “if I needed to”.
How closely will the proceedings mirror Mr Clinton’s trial?
Mr McConnell has said his plans mirror how Mr Clinton’s impeachment trial was conducted in 1999. Democrats point out that while procedures for Mr Clinton’s trial enjoyed bipartisan support, Mr McConnell’s plans likely will not.
House Speaker Nancy Pelosi has appointed seven impeachment managers, compared with the 13 managers named for Mr Clinton’s trial. The seven House Democrats represent a more diverse group than those in the Clinton trial, who were all white men.
Pelosi’s impeachment managers
As the chair of the intelligence committee, Mr Schiff was the de facto leader of last year’s House impeachment probe. A longtime ally of Ms Pelosi, the congressman from California is a former prosecutor who led the case against Richard Miller, a former FBI agent convinced of espionage.
As chair of the House judiciary committee, Mr Nadler led the formal drafting of the articles of impeachment against the president, and was also a central figure in the Mueller investigation into alleged Russian interference in the 2016 US election. A member of Congress from New York since 1992, Mr Nadler has a long history of opposing Mr Trump.
The California legislator will have a leading role in her third impeachment, having been a House staffer during impeachment proceedings against Richard Nixon in the 1970s and a member of the House judiciary committee during Mr Clinton’s impeachment.
The New Yorker became chairman of the House Democratic caucus earlier this year, at the start of his fourth term in Congress. Widely seen as a rising star within the party, Mr Jeffries, who worked as a litigator in private practice before running for elected office, is also a member of the House judiciary committee.
The Floridian, who is currently serving her second term as a member of Congress, sits on two committees that were central to the House impeachment probe: the House intelligence committee and the House judiciary committee.
Mr Crow is a first-term congressman from Colorado and a member of the House armed services committee. An army veteran and lawyer, Mr Crow successfully defeated a Republican incumbent in 2018 to represent a swing district in the suburbs of Denver.
Another first-term member of Congress, Ms Garcia is a member of the House judiciary committee and a former member of the Texas state senate.
What role will the chief justice play?
Mr Roberts will preside over the trial. He is a conservative appointed in 2005 by George W Bush, but has sought to protect the reputation of the Supreme Court from accusations of partisanship. When the senators are locked 50-50 on any motion, Mr Roberts can cast a decisive vote, but it is unclear whether he would take a position.
Will Trump be convicted?
Barring some unforeseeable development, there is almost no chance Mr Trump will be convicted. While many Republicans bristle in private at his actions, particularly over Ukraine, they are worried about the consequences for their own re-election if they vote to convict a president who is exceptionally popular with the party’s base.
Will the trial have any impact on the 2020 elections?
If the Democrats succeed in calling witnesses, they will create another dramatic scene on Capitol Hill to remind voters about Mr Trump’s behaviour over Ukraine. That would give them ammunition to help lure independents in November.
Mr Trump will probably use any acquittal to argue that the Ukraine investigation was a hoax created by Democrats to stop him from getting a second term.
That would have a big impact on the four remaining senators in the race – Elizabeth Warren, Bernie Sanders, Amy Klobuchar and Michael Bennet – who will have little ability to campaign since they will have to remain in Washington six days a week for the trial. That may benefit Mr Biden and Pete Buttigieg, the former mayor of South Bend, Indiana, who with Mr Sanders and Ms Warren make up the top four contenders.