The Senate trial of US President Donald Trump is about to begin.

And at the end of it, 100 US senators will decide whether they should acquit Mr Trump and let him finish his first term, or convict and remove him from office.

But unlike the vote to impeach the President in the House of Representatives, which lasted hours, the Senate trial is likely to last weeks — anywhere from two to five.

And notably, this time is when Mr Trump gets to defend himself from allegations that he used the power of his office to pressure a foreign country to investigate his political rival.

Here’s what to expect as it all plays out (or tap here and we’ll take you to where the trial is at right now).

The first of these is Senate Majority Leader Mitch McConnell. Think of him as the unofficial boss of the Republican Party in this process.

Leader McConnell is important because he’ll have a huge say in exactly *how* this trial will be run. Sure it will be the 100 senators who have the final say. But Leader McConnell commands almost absolute loyalty from the 53 Republicans in the chamber.

And in case you were wondering how he feels about this whole process, here’s what he had to say about it:

The framers built the Senate to break these kinds of partisan fevers. To stabilize our institutions and protect our country. To stop short-term passions from destroying our long-term future. That is the Senate's duty. That is what we must do when this trial begins. — Leader McConnell (@senatemajldr) January 16, 2020

Next are the impeachment managers, who act like the prosecution in a regular court case.

They’re seven Democrats members from the House of Representatives. It’s their job to make the case for why Mr Trump should be removed from office. They are:

Adam Schiff

Jerrold Nadler

Hakeem Jeffries

Val Demings

Jason Crow

Sylvia Garcia

Zoe Lofgren

Acting as the defence for Mr Trump will be:

Pat Cipollone, the White House Counsel

Jay Sekulow, one of the President’s personal lawyers

Jane Raskin, one of the President’s personal lawyers

Pam Bondi, the former attorney-general for Florida

Ken Starr, the head investigator for former president Bill Clinton’s impeachment

Robert Ray, a prosecutor who also worked on the Clinton trial

Alan Dershowitz, a constitutional lawyer known for defending OJ

It’s their job to make the case the President should be acquitted.

The managers and Mr Trump’s defence will be making those cases to 100 US senators, who act as the jury in the case. At the end of the trial, they’ll be tasked with voting to acquit or convict Mr Trump.

The senators are also in charge of setting the agenda for the trial – including a crucial vote on whether to allow witnesses.

At the impeachment trial of president Bill Clinton, senators voted 100-0 to approve the rules of the process. Don’t count on today’s 100 senators showing similar bipartisanship. Here’s Senior Fellow at the US Studies Centre Bruce Wolpe:

“[In 1999] they went into the old Senate chamber, without any staff, and they worked it out. I don’t think you’ll see anything like that,” he said.

Finally, the man watching over all of this will be Chief Justice of the Supreme Court John Roberts. You’ll see him at every day of the trial, but his role is mostly ceremonial.

The trial starts with opening arguments

These will begin in the early hours of Wednesday AEDT.

Expect the Senate to kick things off by passing something called an organising resolution.

Molly Reynolds, a senior fellow with the Brookings Institute, says this document sets the tenor for how the whole trial will proceed.

While the Senate has rules that are written down for how an impeachment trial works, they are terribly under-detailed and we don’t have that many previous experiences of presidential impeachment trials,” she said.



“The result is a little bit more uncertainty, which is an unusual thing not just for people observing the Senate, but for senators themselves.”

Some reporting suggests they’ll do the debating on this resolution in private, before Wednesday, so they can move swiftly on to the next step: opening arguments.

It’s tough to predict how long this step — and every following step — will last because of the variables and the general lack of precedent. Some might last a day, several days, or up to a week.

The opening arguments could get lengthy because this is when the seven impeachment managers will get their chance to lay out why they think Mr Trump should be convicted and removed from office.

The defence then outlines why Mr Trump should be acquitted.

Senators aren’t allowed to talk and they’ve got to hand in their phones at the start.

Once both sides make their case, the senators will be allowed to ask the managers and the defence questions by writing those questions on paper and submitting them to the Chief Justice, who then asks them on their behalf.

After that, we hit a crucial point

There will be two big pushes you’ll want to keep an eye on:

A motion to dismiss the trial completely

Motions to call witnesses before the trial and admit new evidence

The motion to dismiss will come from Republican senators. It’s a move to essentially toss the case out without even voting on it. Mr Trump has called for this to happen in recent weeks, but it certainly doesn’t seem likely to happen at this point, with enough Republican senators speaking out in favour of letting the trial run its course.

Ms Reynolds said that, technically, this vote could happen at any time, but the Republicans appear keen on following the Clinton precedent, which ultimately saw the trial all the way through to a final vote.

The motions to call witnesses or admit new evidence will come from Democrats.

This is the really interesting one, because it will need four Republicans to vote with Democrats to make it happen. Three (Mitt Romney, Lisa Murkowski and Susan Collins) have given indications that they’d like to hear from witnesses like former National Security Advisor John Bolton. Democrats will be working hard to find a fourth.

But this move could also add another wrinkle to the trial, and allow Republicans to call Joe Biden, his son Hunter (for a whole recap on that issue head here) or House Democrats to testify as witnesses as well.

“It’s not Hunter Biden who is on trial, it’s President Trump who is on trial,” Mr Wolpe said.

“Nevertheless, the question is … could Hunter Biden as a witness hurt the Democratic case? It is possible if he is treated in a hostile fashion that extracts damaging information about what he did, that could undercut the case.”

At Bill Clinton’s impeachment trial, witnesses were deposed in closed-door sessions that were taped. It’s unclear if things will play out the same way this time around.

The final vote

Once the witnesses have been called (or not), senators will begin their deliberations.

Each of the 100 senators will get 15 minutes to talk. It’s all behind closed doors, but at the Clinton impeachment trial, senators were able to vote to have their speech added to the congressional record.

After that, it’s finally vote time.

If two-thirds of senators (67) vote to convict the President, he’s immediately removed from office and Vice President Mike Pence is sworn in shortly after. If that happens, senators can also vote again to ban Mr Trump from holding elected office in the future.

But if the number is any less than that, Mr Trump is acquitted. He remains as President and serves the rest of his first term in office.

Don’t forget, it’s not just impeachment happening right now

This impeachment trial is historic. It’s only the third time one has ever been conducted in the history of the United States.

But there are times when it could be relegated to background noise over the next few weeks.

While all of this plays out, there will be:

Several key voting days in the 2020 Demoratic primary

President Trump’s State of the Union Address

Democratic primary debates

Rallies from President Trump

Mr Wolpe says we’re heading into a “split-screen presidency”, where impeachment proceedings play out alongside the frantic beginnings of a presidential election year.

And despite everyone, including Mr Wolpe himself, expecting this trial to end in an acquittal for Mr Trump, he suggested taking any declarations of victory with a grain of salt.

“We will only know if impeachment hurt the Democrats on November 4th (election day) when we know if Nancy Pelosi is still speaker, if Mitch McConnell is still Republican leader and if Donald Trump is still President.”

–ABC