Anthony Zurcher
BBC North America reporter

Donald Trump’s legal team was anticipating their defence of the former president would wrap up later today. Instead, there are numerous new hurdles their client will have to pass before he can receive a final verdict.

The worst-case scenario for Trump is that the call for witnesses opens a floodgate of individuals coming out with new information about the then-president’s actions - and state of mind - during the riots.

His reported phone call with House Minority Leader Kevin McCarthy suggests a callousness, if not a celebration, of the ongoing violence, which is exactly the point House impeachment managers were trying to make when they argued that he intended to incite the attack.

Could that push some of the Republican senators who seemed ready to vote not guilty back onto the fence? Perhaps.

Even in a worst-case scenario, however, there are still 44 Republican senators on the record voting that the trial itself was unconstitutional and illegitimate.

That is the ace in the whole for Trump’s defence team. No matter what new information comes out, there may be at least 34 Republicans - enough to block conviction - who will disregard whatever new information comes to light.

The upper chamber of Congress is well known for taking things slow, and for being late.

So they're being true to form right now - running 15 minutes behind and counting.

As we wait to see who - if anyone - will be called to the stand, here's some of the names that are being batted around for consideration on both sides.

Democratic impeachment managers may call:

• Congresswoman Herrera Beutler, who released details of a call between Trump and McCarthy on Friday night. She was one of 10 Republicans in the House to vote to impeach Trump.
• Mark Meadows, Trump's former chief of staff. He was with the president on the afternoon of 6 January and under oath would have to reveal how aware the former president was of his vice-president's whereabouts and pleas to call in the national guard.

And Trump's defence team may call:

• Speaker of the House Nancy Pelosi "to answer the question as to whether or not there was credible evidence of pre-planned violence before President Trump spoke", tweeted Lindsay Graham on Saturday.
• Vice-President Kamala Harris is on the list of witnesses reportedly being considered by the Trump team. They accuse her of using similar strong political rhetoric in support of Black Lives Matter protesters, and would attempt to draw a comparison to her words and Trump's.

An image has been circulating of a supposed 301-person list of witnesses that the Trump team says they will try and call.

Image source, Getty Images

Despite earlier reports from his counsel that Trump has been in a great mood, things have apparently soured for the former president and his defence team.

And now Trump himself is getting angrier, New York Times Washington correspondent Maggie Haberman reports. The week has been a slog, her sources tell her.

His legal team was already fighting amongst themselves before today's surprise trial extension.

CBS News, the BBC's US partner, confirmed that lawyer David Schoen had apparently quit on Thursday over a squabble over videos that the team was using as evidence. He only rejoined at the request of Trump.

What happens now is up in the air. ABC News reports the legal team had pulled it together for what they believed would be a speedy end to the trial.

There was apparently a brief spat between two Republicans moments ago on the Senate floor.

Ron Johnson seemed to squabble with Mitt Romney, one of the five Republicans who voted in favour of witnesses earlier this morning.

Reporters in the room said they saw Johnson point at Romney and heard him say the words "blame you". The back-and-forth between the two lawmakers was reportedly heated, with voices raised.

When asked by a pool reporter about what was said, Johnson replied that "those are private conversations" and it was "grotesque" that the media was recording it.

Of course, as journalists on Twitter have been pointing out, their seemingly fiery discussion happened in a very public setting.

Image source, Getty Images

The action will resume at 12:30 ET (17:30 GMT), when we will learn more about how this new and unexpected chapter of the trial - the calling of witnesses - will work out.

Image source, Getty Images

With the Senate in a prolonged recess, let's take a look at some of the figures who made headlines this week. With the former president absent, there has been plenty of room for others to shine.

• Joe Neguse, at 36, is the youngest house impeachment manager and the first black congressman from his state. His calm and steady demeanour in presenting the prosecutions' evidence has raised the Colorado congressman's profile nationwide.
• Stacey Plaskett, who represents the US Virgin Islands, is the first delegate to serve on an impeachment team. That means she represents a US territory, not a state. So she does not have a vote on the House floor but has still been able to present evidence against him. She made headlines for speaking passionately about her experience as a young black girl growing up.
• Bruce Castor, Trump's last-minute pick to defend him, made headlines for his rambling opening statement on Tuesday and drew ire from both sides of the political spectrum. He took note of the criticism and came back Friday with a much clearer and coherent argument in defence of the former president.
• Officer Eugene Goodman is once again in the news. The Capitol officer was deemed a national hero as video of him fending off the mob surfaced. This week, new video aired that shows how narrowly this same mob missed Senator Mitt Romney, amplifying Goodman's heroic status.

Read more about the heroics of Officer Goodman

The BBC's Gary O'Donoghue explains how new evidence in the last 24 hours led to the unexpected decision to call witnesses.

The Senate is now going to debate on the rules around witnesses - how many can be called and in what fashion, he explains.

Watch his full explanation:

Now attention has turned back to the events of 6 January, it's worth taking a look at how the trial has shed fresh light on what happened.

The prosecution's aim was to prove Donald Trump egged on the mob to attack the Capitol.

To do this, they gave a very detailed hour-by-hour account of how the day unfolded, both at Congress and at the White House.

They argued that Trump's words directly led rioters to the Capitol, and they homed in on how long the former president waited to condemn the attacks.

Read the full timeline of the day's events here.

Anthony Zurcher
BBC North America reporter

Image source, Vince Bucci/AFP via Getty Images

A year ago, with Republicans running the process, the Senate decided not to call any witnesses in Donald Trump’s first impeachment trial.

To find some precedent for what the Senate is now considering in Trump’s second impeachment trial, senators will have to look back to Bill Clinton’s impeachment in January 1999.

During those proceedings, the Senate voted to issue several subpoenas, including of Clinton officials and star witness Monica Lewinsky, whose testimony was recorded and presented later in the trial.

It took more than a week for that process to unfold.

The Senate later voted overwhelmingly to not request that Lewinsky testify in person. And in the end, Clinton was acquitted of both charges.

There's a recess now and quite a bit of confusion as to where the trial is headed. One thing is certain - it's all going to take longer than was thought when we woke up this morning.

The Senate will have to vote, by a simple majority, to subpoena specific witnesses, CNN's Manu Raju explains on Twitter., external

If they vote to subpoena a given witness, they will have to depose them first, which will slow the trial down.

After the witnesses are deposed, the chamber will have to set new guidelines on how to handle the testimony, he continues.

Image source, Getty Images

Strong, punchy, a fighter.

Michael van der Veen is exactly the type of lawyer that Trump wants defending him in this trial.

"I should take my own advice and cool the temperature," he said this morning on the Senate floor after getting riled up from his own opening statement.

When the Senate broke out in laughter over his suggestion to conduct depositions at his office in Philadelphia, he defensively shouted: "I haven't laughed at any of you!"

Barbara Plett Usher
BBC News, Washington

Senators had appeared close to resolving the trial after the defence wrapped up its arguments on Friday.

But there were still unanswered questions about when and what the president knew as the attack unfolded.

And then a House Republican offered new details about a phone call between Trump and the House minority leader.

Democrats say this shows the former president’s indifference to the violence.

They have voted to hear from the congresswoman before proceeding. It’s not clear how many other witnesses may be called and how long this will take.

Image source, Getty Images

Let's break down what we know about this one phone call that's changed the course of the trial.

Who was involved?

The call itself was between Republican Congressman Kevin McCarthy, the House minority leader, and then-President Trump.

But we heard about it from Republican Congresswoman Jaime Herrera Beutler, who was one of 10 conservatives to vote in favour of impeaching Trump.

Who said what?

Beutler offered her recollection of a conversation she had with McCarthy regarding the call.

She said that when McCarthy called Trump during the riot, he asked the president to call off his supporters.

Initially, Trump suggested it was all being done by left-wing anarchists. When McCarthy pushed back, Trump reportedly told him: "I guess these people are just more angry about the election and upset than you are."

That apparently sparked a shouting match, CNN reported on Friday, with McCarthy furiously telling Trump: "Who the [expletive] do you think you are talking to?"

Why does this matter?

Following that vote on witnesses, it looks like Democrats may be able to bring Beutler in for a deposition as well as request her notes on the matter.

This will extend the trial's duration as lawmakers seek to gain more insight into the important question of what exactly was going through Trump's mind that day.

And if it emerges that the president wasn't as "horrified" over the events of 6 January as his defence has said, that could sway more Republicans to join Democrats when it comes to conviction.

Anthony Zurcher
BBC North America reporter

There was always the chance that the House impeachment managers would vote to call witnesses, although it seemed like few in the Senate - Democrats included - were interested in continuing the trial past this weekend.

That all changed on Friday night, however, with the reports of an angry phone call between Donald Trump and House Minority Leader Kevin McCarthy as the 6 January riots were unfolding.

Now Democrats want to delve deeper into the contents of that call, which could shed light on the former president’s attitude toward the violence.

Did he sympathise with the mob? The call, Democrats seem to believe, might be the key.

The Democrats, along with five Republicans, have won a vote to call witnesses. Reaching a simple majority, the measure has passed and witnesses will be called.

Image source, Getty Images

We're seeing some - slightly heated - back-and-forth on the floor now between Raskin and van der Veen regarding calling witnesses.

Essentially, the House wants to call at least one new witness (Congresswoman Beutler) while Trump's defence prefers a speedy end to this trial - or else, they'll want to call dozens of witnesses.

After both sides finish presenting their case, it will be time for the senators to debate the matter.

A simple majority vote in the evenly split chamber will then decide whether or not witnesses are called.

And of course, all this means today's trial proceedings will take longer than previously anticipated, so get settled in.

House impeachment manager Jamie Raskin has asked to subpoena Republican Jaime Herrera Beutler and her notes, believing there may be new evidence about a phone call between Trump and McCarthy on 6 January.

Anthony Zurcher
BBC North America reporter

For weeks, Mitch McConnell has been the Hamlet of these impeachment proceedings, seemingly giving conflicting messages about how he viewed the ongoing drama in the Senate.

He made public comments condemning Donald Trump, but when the time came for early votes he sided with the defence.

It appears that drama is now over, as the Senate minority leader is reportedly circulating a letter to Republican colleagues saying he will vote against conviction.

In doing so, McConnell demonstrates that he knows that the centre of gravity among Senate Republicans sits with acquittal - and with it, he dashes Democratic hopes that he could lead a late move to sway his partisan colleagues to turn against the ex-president.

With a prayer from the chaplain and the Pledge of Allegiance, day five of the Trump impeachment trial is under way.