The question of whether to allow new witnesses and evidence became one of the central debates of the trial.

Republicans had been keen for a speedy trial with no witnesses or new documents. Democrats wanted to bring in both. They said there was fresh evidence available that hadn't been heard in the first part of the investigation, in the House.

Democrats had hoped to win the vote for new witnesses, which would have brought additional testimony to the senators - and to the public. They only required a simple majority in the vote of witnesses - so only four Republicans would have needed to defect.

The calls for witnesses were reinvigorated after the New York Times cited a leaked manuscript from former National Security Adviser John Bolton's new book, that said Trump told him he wanted to freeze aid to Ukraine until Kyiv helped with investigations against the Democrats, including former Vice-President Joe Biden.

If the reports about Mr Bolton were true, and he were to testify to that effect, he would be the first witness in the process to directly link the president to an alleged quid pro quo (exchange of favours) with Ukraine and an abuse of presidential power.

Mr Trump has denied the claims - while his lawyers have argued that the allegations in any case did not amount to an impeachable offence.

In the end, as expected, the motion for witnesses was denied by 51 to 49. Mitt Romney, and Susan Collins, were the two Republicans who sided with the Democrats.

By a thin majority, US senators have agreed not to call witnesses during Donald Trump's impeachment trial.

This paves the way for the swift end of the trial, that is all but certain to end in Mr Trump's acquittal.

Senators are now casting votes for whether or not to call witnesses. There are only 100 senators - so watch this space - we should have the outcome very soon.

One of the moderate Republicans who may at one point have voted for witnesses, Tennessee senator Lamar Alexander, is likely not to do so.

Interestingly, he did not say he believed Donald Trump had not sought favours from Ukraine, or tried to block Congress' investigation.

He said Democrats had proven the case against Trump but that the president's actions did "not meet the United States Constitution's high bar for an impeachable offence".

Is this typical?

Even though Donald Trump is the second most popular president among his own party members (89% of whom approve of his performance, according to Gallup), it doesn't mean all Republicans think he's blameless.

In a poll conducted by the Associated Press and the NORC Center for Public Affairs Research last week, only 54% of Republicans believed he had done nothing wrong.

We're awaiting a vote sometime soon on whether witnesses will be allowed at the trial.

Here's what we know:

• a simple majority, of 51 senators, need to agree
• 51 Republicans are likely to vote against allowing witnesses
• 49 senators (45 Democrats, two independents and two Republicans) are likely to vote for witnesses
• Utah senator Mitt Romney and Maine Senator Susan Collins - are the two Republicans likely to vote alongside Democrats

Image source, CBS

Adam Schiff has finished making his case. Now, senators are standing around on the floor, speaking in small groups.

Commentators think they are waiting around and discussing whether to go to a vote on witnesses now.

On the Democrats' side, Adam Schiff is wrapping up the case that witnesses should be called.

He points out that if the Senate votes for witnesses, the president's team could call and question them as well.

Then he urges senators to think independently. "You have the sole power to try this case. You do not have to allow the president's lawyers to abuse this trial, or your process. You have the power to decide."

He ends by quoting John Warner, a former Republican senator who issued a statement today urging senators to vote for witnesses.

"Not only is the president on trial, but in many ways so is the Senate itself.

"Throughout the long life of our nation, federal and state judicial systems have largely supported the judicial norms of evidence, witnesses and relevant documents. I respectfully urge the Senate to be guided by the rules of evidence and follow our nation's judicial norms... by welcoming relevant witnesses and documents as part of this impeachment trial."

Image source, Getty Images

House Manager Adam Schiff is now speaking.

"Some things are just as simple as they appear," he says. "A trial without witnesses is simply not a trial. You can call it something else, but it's not a trial."

Image source, EPA

Speaking in the chamber, Trump's personal lawyer Jay Sekulow outlined the defence's case against calling witnesses.

He accused the Democratic impeachment managers - the prosecution - of doing a poor and rushed job, saying the managers had "not proven their case by any stretch". He told senators that House Democrats had "got their wish of an impeachment by Christmas ... but now they want you to do the work they failed to do".

Calling witnesses would lead to a long, drawn-out trial, Sekulow said, attempting to rebut a Democrat argument that witnesses could be heard from within a week. "If we go down the road of witnesses, this is not a one week process," he said.

And he argued that even if witnesses were called, the original allegations were not serious enough to warrant removal from office anyway.

With that, Trump's defence has finished for now, and the lead Democratic impeachment manager, Adam Schiff has 30 minutes to sum up the prosecution arguments on calling witnesses. Schiff is up now.

Trump counsel Patrick Philbin says there is no need for new witnesses, "because these articles of impeachment on their face are defective".

Philbin says the charge of abuse of power focuses on "subjective motives", claiming the president defied US foreign policy.

"The theory of abuse of power that they've framed ... would do grave damage to the separation of powers under our Constitution because it would become so malleable they can pour into anything they want to find illicit motives for some perfectly permissible action."

Philbin adds that the Constitution "limits and constrains the impeachment power". But the Constitution is rather vague about impeachment. Article II states a president can be removed for "treason, bribery and high crimes and misdemeanours", but does not clearly define those terms.

Trump's counsel has reframed its defence somewhat this week, arguing not that the president did not commit the abuses of power he is accused of, but that any such abuse of power would not be impeachable in the first place.

• The case for and against impeachment

Image source, Getty Images

Image source, Getty Images

The White House argues that the trial against President Donald Trump is invalid because he has not committed any crimes. But the argument is deeply flawed, writes legal scholar Jonathan Turley.

Forty-five years ago, Cowboys quarterback Roger Staubach said: "I closed my eyes and said a Hail Mary." The so-called Hail Mary pass is now a mainstay of American football where a quarterback, in the final seconds of a close game, throws the ball into the end zone on a hope and a prayer.

The White House has decided to frame its defence around a constitutional Hail Mary pass in arguing that the impeachment itself is invalid because articles of impeachment must be based on alleged criminal acts. The "quarterback" in this play is Harvard Professor Alan Dershowitz who believes that the Senate should simply dismiss the case as constitutionally invalid.

The problem is that this pass is not going into the constitutional end-zone but well beyond the stadium.

The argument is based on a literal reading of the standard "high crimes and misdemeanors." Those are criminal terms, to be sure, but they were never viewed as such in England, where the standard was first forged, nor in the United States in past judicial and presidential impeachments.

American impeachments stand on English feet and English impeachments often stood on non-criminal allegations.

Read Jonathan's full analysis here.

Top Democrat Jerry Nadler, one of the impeachment managers from the House of Representatives who has been making the case against Trump, will be missing the rest of the trial.

He announced on Friday that he needed to remain at home with his wife, who is battling cancer, but had faith in his colleagues.

Image source, Getty Images

There is still nothing happening on the Senate floor - this adjournment is now nearly as long as the working session that preceded it.

While they're at ease, we can bring you some of our best explainers on the story.

WHAT HAPPENED THIS WEEK: Here's a recap on the trial so far

FIVE POSSIBLE TWISTS: Think it's a foregone conclusion? Perhaps not

JOHN BOLTON: Why does everyone want to talk to him?

SIMPLE GUIDE: If you want a basic take on what's going on

GO DEEPER: Here's a 100, 300 and 800-word summary of the story

IMPEACHMENT QUESTIONS? We’ve got answers

CONTEXT: Why Ukraine matters to the US

Tara McKelvey
BBC News White House reporter

Image source, Getty Images

Democrats have intensified their calls for former US National Security Adviser John Bolton to testify in President Donald Trump's impeachment trial.

Bolton, a Republican, is an unlikely hero for Democrats. Still, they believe he will act as a star witness, one who will provide irrefutable evidence of wrongdoing by Trump and help bolster the case for his removal from office.

Democrats once invested similar hopes in another Washington figure, Robert Mueller, the former special counsel.

Bolton could be different - or so Democrats hope.

Yale-educated Bolton, 71, was national security adviser from 2018-19.

He was "personally involved" in the president's dealings with the Ukrainian officials, according to Bolton's lawyer.

The former national security adviser was "at the nerve centre for all important decisions", says Matthew Spence, a former deputy assistant secretary of defence.

Read Tara's full analysis here.

During a brief recess in the trial, Schumer tells reporters there is no deal with McConnell.

But he says lawmakers owe it to their constituents to explain why they're voting a certain way, and there must be a debate.

"We are going to use whatever power we have to prevent [the vote] from being rushed through, but right now there is no agreement," he says.

Image source, Getty Images

In a word - yes.

The Senate has allowed witnesses in every other impeachment trial, including the only other presidential trials of Andrew Johnson and Bill Clinton.

(Monica Lewinsky, the former White House intern involved in the Clinton impeachment pointed out the same earlier today on Twitter.)

Republicans have argued that the House of Representatives didn't do an adequate job subpoenaing witnesses before passing the buck to the Senate. They also say calling witnesses will take too much time away from legislative work.

Democrats have responded that the Constitution doesn't set limits on which chamber can call witnesses, and have accused Republicans of not doing their duty to impartial justice.

Speaking on the floor just now, lead impeachment manager Adam Schiff warned that having no witnesses will set a dangerous precedent.

Image source, Getty Images

Former White House Chief of Staff John Kelly told news site NJ.com, external on Friday a trial without witnesses is only "half a trial".

"If I was advising the United States Senate, I would say, 'If you don’t respond to 75% of the American voters and have witnesses, it’s a job only half done," he said. "You open yourself up forever as a Senate that shirks its responsibilities."

Kelly, a retired Marine general, left his post last January after his relationship with Trump reportedly deteriorated.

Republican congressman Andy Biggs, a Trump ally, was quick to respond, saying lawmakers heard from a majority of witnesses.

NBC News is reporting that Republican Senate leader Mitch McConnell and his Democratic counterpart Chuck Schumer have agreed to have a Wednesday vote to acquit Trump.

The leaders told their party members this during closed-door lunches. If it's approved, the trial will resume on Monday for closing arguments.

The White House had wanted an acquittal vote prior to the State of the Union on Tuesday night, but an official told NBC correspondent Leigh Ann Caldwell: "We're happy with an acquittal as soon as possible."

"Whenever the date and time lands, resolution provides conclusion."

What do Democrats get out of this? If the trial wraps up on Tuesday, it means Democratic presidential hopefuls can get back on the campaign trail.