Donald Trump on Tuesday will become the first US president to face two impeachment trials.

Trump was impeached last month on one charge of inciting an insurrection for his role in the January 6 siege on Capitol Hill that left five people dead. Hours before a mob of his supporters stormed the legislature, the then-president told the crowd: “If you don’t fight like hell, you’re not going to have a country any more.”

This is the Financial Times guide to the trial:

The constitution provides scant detail on how an impeachment trial should be conducted in the US Senate, but notes that when the president is tried, the chief justice of the Supreme Court “shall preside”. Chief Justice John Roberts presided over Trump’s first impeachment trial last year, when senators exonerated him on two charges relating to his efforts to get the Ukrainian president to investigate Joe Biden.

This time around, with Trump as a private citizen, the president pro tempore of the Senate, Patrick Leahy will preside instead. President pro tempore is the second highest-ranking member of the Senate, and third in the line of presidential succession, behind the vice-president and Speaker of the House.

Leahy, a Democrat, has said he will preside objectively over the trial, which will begin on Tuesday with opening arguments from both impeachment managers and Trump’s legal team.

Republican lawmakers and Trump’s legal team have argued that it is not constitutional to try a former president after he has left office. Trump was impeached while he was still in the White House, but will be a private citizen during his trial.

Most legal scholars contend it is constitutional for the trial to be held. In an open letter published last month, more than 150 academic experts, including the co-founder and several members of the conservative Federalist Society, said the constitution “permits the impeachment, conviction, and disqualification of former officers, including presidents”.

The impeachment managers and Trump’s legal team last week filed briefs setting out the arguments they will make in the trial.

The impeachment managers said the evidence was “overwhelming” that Trump had “singular responsibility” for the “tragedy” at the Capitol, adding: “It is impossible to imagine the events of January 6 occurring without President Trump creating a powder keg, striking a match, and then seeking personal advantage from the ensuing havoc.”Trump’s lawyers repeated their claims that a trial would be unconstitutional, and argued the former president “at all times . . . fully and faithfully executed his duties as president of the United States”. They said Trump had “exercised” his free-speech rights under the First Amendment of the Constitution to “express his belief that the election results were suspect” in the run-up to the siege.

Lead impeachment manager Jamie Raskin last week invited Trump to testify under oath, something the former president’s lawyers, Bruce Castor Jr and David Schoen, swiftly rejected.

“Your letter only confirms . . . you cannot prove your allegations against the 45th president of the United States,” Trump’s lawyers wrote.

“Any official accused of inciting armed violence against the government of the United States should welcome the chance to testify openly and honestly — that is, if the official had a defence,” Raskin said in response. “We will prove at trial that President Trump’s conduct was indefensible. His immediate refusal to testify speaks volumes and plainly establishes an adverse inference supporting his guilt.”

The constitution stipulates “no person shall be convicted without the concurrence of two-thirds of the members present”. Because the 100-member chamber is split, 50-50, at least 17 Republicans would need to find Trump guilty in order for him to be convicted, assuming all senators participate.

That outcome is widely seen as extremely unlikely, after all but five Republican senators backed Trump in a procedural vote last month that called into question whether a trial was constitutional.

“I think it is pretty obvious from the vote . . . that it is extraordinarily unlikely that the president will be convicted,” Susan Collins, the Republican from Maine, told reporters after the procedural ballot. “Just do the math.”

Collins is one of the five Republicans who sided with Democrats in saying the trial would be constitutional.

Others, including Senate minority leader Mitch McConnell, voted in favour of the motion but said they would not prejudge the result.

It remains possible that several senators could abstain from a vote rather than cast a verdict one way or the other, therefore reducing the number of jurors “present” in the chamber and, in turn, the number of votes needed to convict.

If Trump were convicted, the Senate could hold a simple majority vote to bar him from holding public office in future. That would have significant implications for 2024, when Joe Biden will be up for re-election, given Trump has already said he is considering running for president again.

Some Washington operatives argue the impeachment trial could backfire on Democrats, dominating Biden’s crucial first 100 days in office and risking interfering with his legislative agenda, which includes a proposed $1.9tn coronavirus relief package. Critics say voters will see the trial as a waste of time at a moment when Americans are struggling to make ends meet and looking for support from lawmakers.

But others see the trial as full of potholes for elected Republicans, who will want to try to take back control of the House and Senate in the 2022 midterms. That will require the party to energise Trump’s conservative base while winning back moderate suburban voters who deserted the party in the Trump era. Opinion polls show these voters are more likely to support punishing the former president.

The Cast

IMPEACHMENT MANAGERS

Jamie Raskin: The Democratic congressman from Maryland and former constitutional law professor will be the lead manager, in charge of making the case against Trump. Raskin, whose 25-year-old son died by suicide just one week before the Capitol Hill siege, said in an emotional television interview last month: “I am not going to lose my son at the end of 2020 and lose my country and my republic in 2021.”

Diana DeGette: The veteran Democratic congresswoman from Colorado was first elected to Congress in 1996 after a career as a lawyer and state legislator.

David Cicilline: The Democratic congressman from Rhode Island was the mayor of Providence, Rhode Island, before being elected to Congress in 2010. A trained lawyer, he chairs the House judiciary subcommittee on antitrust, where he has proposed breaking up big tech companies.

Joaquin Castro: The Democratic congressman from Texas and chair of the Congressional Hispanic Caucus was a litigator and state legislator before being elected to Congress in 2012. His identical twin brother, Julián Castro, was a member of Barack Obama’s cabinet and ran for president last cycle before dropping out ahead of the Iowa caucuses.

Eric Swalwell: The Democratic congressman from California and gun control advocate ran for president in the last cycle, memorably calling on Joe Biden to “pass the torch” to a new generation of leaders in a Democratic primary debate. He later dropped out of the race.

Ted Lieu: The third-term Democratic congressman from California was a state legislator before being elected to Congress in 2014. He was among Trump’s most vocal critics on social media throughout his four years in the White House.

Stacey Plaskett: The Democratic congresswoman, who grew up in New York and is the child of parents from the US Virgin Islands, is a lawyer and former congressional staffer who is now the delegate to the House of Representatives from the US Virgin Islands.

Madeleine Dean: The Democratic congresswoman is serving her second term representing Pennsylvania’s fourth congressional district, which covers most of Montgomery County, a suburban area north of Philadelphia where voters turned out in large numbers against the president in November. A trained lawyer, she was an English professor at La Salle University before running for Congress.

Joe Neguse: The Democratic congressman from Colorado is serving his second term in the House, where he sits on the judiciary committee.

TRUMP LAWYERS

David Schoen: The experienced trial lawyer has offices in New York and Montgomery, Alabama, and describes himself primarily as a civil rights attorney. He represented Trump ally Roger Stone, who was convicted of crimes relating to the Mueller investigation before being pardoned by Trump in December. Schoen has said he was meant to meet Jeffrey Epstein shortly before his death, but had to reschedule, and that he believes Epstein was murdered.

Bruce Castor, Jr: The longtime prosecutor and former Republican politician from Montgomery County, Pennsylvania — the same area Dean represents — was appointed solicitor-general of Pennsylvania, a role he held for six months in 2016 before becoming the state’s acting attorney-general. Now in private practice, his reputation took a hit in 2016 when he testified about his 2005 decision to not prosecute Bill Cosby, the TV star who was later convicted of several sexual offences.