Although the trial ceremonially began on Thursday, its substantive proceedings are scheduled to begin on Tuesday.
While not a criminal trial, the Senate is tasked with deciding whether Trump’s conduct warrants his removal from the office of the President of the United States.
On Thursday, the two articles were read aloud on the Senate floor, and Senators — who will act as jurors — were sworn in by Chief Justice John Roberts, taking an oath to “do impartial justice according to the Constitution and laws.”
Now that the process has moved to the Senate — the upper chamber of Congress — a new series of rules will be put in place to govern the proceedings.
How will the Senate impeachment trial work and what are the rules?
Here’s a look at what’s happening.
What’s at issue
On Dec. 18, Trump became the third-ever U.S. President to be impeached.
Following weeks of investigation, a majority of Congress members in the U.S. House of Representatives voted in favour of impeaching Trump over two charges: abuse of power and obstruction of Congress.
Trump was found to have abused his power by withholding military aid to Ukraine in exchange for the announcement of investigations into former Vice President Joe Biden and his son Hunter‘s work on the board of a Ukrainian energy company, and into unsubstantiated claims that the country interfered in the 2016 U.S. presidential election.
Lawmakers said Trump impeded their investigation by refusing to hand over important documents, and by ordering officials called to testify not to comply with lawful subpoenas.
Trump has vehemently denied any wrongdoing and has repeatedly called the impeachment process a “sham” and a “hoax.”
Rules of engagement
Now that the impeachment process has moved on to the Senate, a strict set of rules will be applied to help to govern the proceedings.
One of the main rules is that Senators must refrain from talking during the trial.
According to historic Senate rules, Senators must “keep silent, on pain of imprisonment,” meaning no talking or debate is permitted in the chamber during the trial.
In a set of decorum guidelines released earlier this week, Senators were reminded that they would have the opportunity for “limited speech,” and that members should “refrain from speaking to neighbouring Senators while the case is being presented.”
Senators are also prohibited from using cell phones or other electronic devices. According to the guidelines, all electronic devices must be left outside of the chamber in the cloakroom.
As well, Senators have been told to only bring reading material that pertains “to the matter before the Senate” to the chamber.
On Wednesday, House Speaker Nancy Pelosi announced the seven members that will act as House managers and will prosecute the case against Trump in the proceedings.
The defence team
Meanwhile, Trump has been assembling his own legal team.
Leading the group is White House Counsel Pat Cipollone and Trump’s personal lawyer Jay Sekulow.
Other members of Trump’s defence team include Ken Starr, the prosecutor whose investigation two decades ago resulted in the impeachment of Bill Clinton and former Harvard law professor Alan Dershowitz.
Pam Bondi, a former Florida attorney general; Jane Raskin who was part of the president’s legal team during Robert Mueller’s investigation; Robert Ray, who was part of the Whitewater investigation of the Clintons; and Eric D. Herschmann of the Kasowitz Benson Torres legal firm, which has represented Trump in numerous cases over the last 15 years, have also been named to the team.
Chief Justice Roberts
U.S. Chief Justice John Roberts, 64, will preside over the trial.
His main role is to keep the process on track. He could, however, be asked to rule on whether certain witnesses should be called to testify. If a majority in the Senate disagrees with a ruling he makes, senators can vote to overturn his decision.
When will it begin?
The trial is set to begin at 1 p.m. ET on Tuesday, and as designated by Senate rules, will run six days per week — Monday to Saturday — until it is finished.
On Tuesday, Senate Majority Leader Mitch McConnell will kick-off the proceedings by introducing a resolution, to set the ground rules of the trial.
McConnell previously said the rules will be structured around those followed during the impeachment trial of Clinton in 1999.
All of the parameters of the trial, including speaking time and potential witnesses, will be laid out during this time.
Once the resolution has been adopted, opening arguments will begin. This is expected to last a number of days.
After opening arguments have been delivered, Senators will be given the opportunity to submit questions to both sides.
Democrats are expected to continue their push to hear from witnesses during the Senate trial.
If McConnell’s resolution on initial trial rules is adopted, as expected, Senators would likely vote sometime after the trial has started on whether to introduce witness testimony sought by the Democrats.
Democrats are seeking testimony from White House Chief of Staff Mick Mulvaney, his senior adviser Robert Blair, former national security adviser John Bolton and Office of Management and Budget official Michael Duffey.
McConnell, however, has lambasted the Democrats over their calls for witnesses, saying it is a “fishing expedition.”
“If the existing case is strong, there’s no need for the judge and jury to reopen the investigation,” he told reporters on Tuesday.
Just last week, though, Bolton said he was “prepared to testify” if subpoenaed by the Senate.
“If the Senate issues a subpoena for my testimony, I am prepared to testify,” he said.
Bolton did not testify before the House.
At the end of the trial, the Senate will hold a vote on whether or not to convict and remove Trump from office.
A two-thirds vote is needed in order for Trump to be ousted.
The Republicans currently hold 53 seats in the 100-seat Senate chamber, meaning all Democrats, both Independents and 20 Republicans in the Senate would need to vote to convict and remove Trump— something experts say is very unlikely.
It is widely expected that Trump will be acquitted by his fellow Republicans, and will remain in office, eligible for re-election.
If two-thirds of the Senate did vote to remove Trump, Vice President Mike Pence would take over the office until the November election.
—With files from Reuters and The Associated Press