Donald Trump, the Republican presidential nominee, twice refused to say he will accept the outcome of next month's election during the third and final television debate with his Democratic opponent, Hillary Clinton. 

Asked by Fox News anchor Chris Wallace if he would accept the result, Trump replied: "I will look at it at the time." 

He added: "I'm not looking at it now.  I will keep you in suspense." 

Clinton said she was "appalled" a major party nominee would take such a position. 

In recent days, Trump has repeatedly claimed the vote will be "absolutely rigged" and Clinton will "steal" the election. 

The suggestion that Trump might reject the result "marked an extraordinary departure from one of the most fundamental principles of American democracy: the peaceful transfer of power after an election", says CNN. 

It also sets the businessman at odds with his running mate, Mike Pence, who said on Sunday that both men would "absolutely accept the result of the election". 

Trump's campaign manager, Kellyanne Conway, tried to play down the comments. 

"Donald Trump will accept the results of the election because he's going to win the election," she said. 

Trump landed some blows on his opponent in last night's debate in Las Vegas, attacking Clinton on trade policy and her record in Washington. 

"In contrast to their two previous debates, the 90-minute discussion covered significant substantive ground," says the New York Times. 

There were personal insults too: Clinton accused Trump of being a "puppet" of Russian President Vladimir Putin, while he said she was a liar, a criminal and "a nasty woman". 

But Trump's refusal to accept the election would be free and fair was effectively the end of the debate, says BBC North American correspondent Anthony Zurcher. 

"At that point, the headlines were written and the debate results were locked in," he says. " It was not a good night for the Republican." 

Missed the debate?  Here's how TheWeek.co.uk live blogged the action:

3.30am: To end the debate, Wallace asks each candidate for a one-minute closing statement.  Clinton goes first: "I'm reaching out to all Americans because we need everybody.  Let me speak directly to the camera.  We need your talents.  I've seen the presidency up close... I have made the cause of children and families my life's work.  That will be my mission.  Families against corporate interests.  Give me a chance." 

Trump follows: "She's raising the money from the people she wants to control.  Doesn’t work that way.  We're going to make America great again.  We have a depleted military.  Take care of our veterans.  Policemen and women disrespected.  Inner cities.. shot walking to the store.  All she’s done is talk to the African Americans and the Latinos.  We are going to make America strong again... it has to start now.  We cannot take four more years of Barack Obama and that’s what you get when you get her." 

So who won?  Twitter users reacted with horror to Trump’s refusal to commit to accepting the outcome of the election, a moment that "could become a defining moment of the campaign," Fox says. 

nothing in this debate, nothing in this campaign, nothing in this country matters as much as Trump rejecting USA's 240 year democratic order — Philip Gourevitch (@PGourevitch) October 20, 2016

The five words that matter most in this debate: "I'll keep you in suspense." —  Lois Beckett (@loisbeckett) October 20, 2016

God @KellyannePolls has just an impossible job. —  Ben White (@morningmoneyben) October 20, 2016

Several Republicans also criticised Trump's comments. 

.@realDonaldTrump saying that he might not accept election results is beyond the pale — Jeff Flake (@JeffFlake) October 20, 2016

He should have said he would accept the results of the election.  There is no other option unless we're in a recount again. —  Laura Ingraham (@IngrahamAngle) October 20, 2016

3.20am: Chris Wallace asks Trump whether he will accept the result of the election. " I will look at it at the time," Trump responds. " Wow," The Guardian says. 

Chris Wallace seems "almost offended by Trump’s answer on not accepting the legitimacy of the election, says The New York Times. 

According to the Guardian, "Trump is increasingly punchy as the night goes on.  Clinton seems to realise that none of this is really dangerous territory for her, for the voters she’s after.  She seems to be leaning back a bit, kind of reclining on her hips.  Looking at him and nodding and blinking as he rants and waves and gestures." 

Next, the candidates discuss Islamic State.  A question for Trump: "Would you use US troops in Syria or Iraq [and] what will happen to Islamic State after the assault on Mosul?" 

Trump replies: "Mosul's so sad.  We had Mosul." 

The businessman argues with both Wallace and Clinton over whether or not he supported the Iraq war, before returning to the Iraqi assault on Mosul.  He says that the only reason Iraq is going into Mosul is because Clinton is running for president. " She wanted to look tough." 

The New York Times clarifies that "it was in February 2015 that the US first started talking about taking Mosul." 

3.10am: Next on the agenda is taxes and the national debt. 

Clinton attacks Trump's economic plans which she says would cost the US 3.5 million jobs. 

The Washington Post's fact checker confirms the claim noting that "a well-respected economist at Moodys Analytics, did issue a report saying that if Trump’s economic plans were fully implemented, 3.5 million jobs would disappear, incomes would stagnate, debt would explode, and stock prices would plummet." 

After a short back and forth, Chris Wallace turns the debate to the question of each candidates' fitness to be president.  He opens with the accusations of sexual abuse that have been made against Trump by numerous women over the past few weeks. 

Trump responds: "Those stories have been largely debunked... I don't know those people.  I have a feeling it was her campaign that did it." 

Clinton keeps "unloading on him," The Guardian says, quoting the Republican candidate's own words back to him. " Donald thinks belittling women makes him bigger... I don't think there's a woman out there who doesn't know what that feels like." 

Wallace then turns to accusations levelled at the Clinton Foundation.  Trump calls the foundation "a criminal enterprise." 

Clinton says she is glad to compare what goes on at her own foundation with the Trump Foundation, which she says is a private slush fund for Trump and once purchased a huge portrait of the businessman. " Who does that?" 

Republican columnist Frank Luntz calls Clinton's response to the legitimate questions about her foundation "a disaster." 

Hillary's Clinton Foundation answer was a disaster.  Trump scored yet again by pointing out its corruption. # debate pic.twitter.com/dgFH3oPg4D — Frank Luntz (@FrankLuntz) October 20, 2016

2:40am: The debate turns to immigration.  Trump opens, reiterating that he wants to build a wall on the Mexican border. " We have some bad hombres here and we are going to get 'em out," he says. 

Clinton goes on the attack, noting that "at [Trump's] meeting with the Mexican president, [he] didn't even mention it [the wall].  He choked." 

Wallace turns to the tranche of Clinton's emails leaked by Wikileaks in which she says, "My dream is a hemispheric common market with open trade and with open borders." 

Clinton clarifies that she was talking about energy not people. " We trade more energy with our neighbours than we do with the rest of the world combined." 

The Secretary of State says that the only reason these emails were published in the first place was because they were hacked by Russia, and attacks Trump for being cosy with Vladimir Putin.  She says Putin ordered the cyber attack "because he'd rather have a puppet as president of the United States." 

Trump responds: "[I'm] no Puppet!  You're the puppet." 

"And Trump is back!"  says Adam Nagourney of the New York Times. 

2.20am: The first topic for discussion is the US Supreme Court.  Clinton opens, saying that she would like the court to represent all people, and clarifies that contrary to Trump's claims, she supports the right to bear arms.  Trump responds that if he becomes president, he will protect the second amendment right to bear arms and will select pro-life justices with "a conservative bent," who will be "great scholars." 

The Guardian notes that Trump has a hoarse voice - "he's croaking."  He is also sniffing again, but he appears to be more composed than he was at the last debate. " This really is the most conventional debate outing for Trump so far," says Maggie Haberman on the New York Times. 

2.00am: Chris Wallace of Fox News gets the debate underway, welcoming the two candidates to Las Vegas. 

Hillary Clinton and Donald Trump arrive on stage and again don't shake hands, going straight to their lecturns. 

The debate will be divided into six sections.  Each 15-minute segment will begin with a question from the moderator followed by two minutes for each candidate's answer and then follow-up questions from the moderator. 

Before the debate began, the New Yorker said that rather than preparing, "an activity that taxes his short attention span," Trump has instead spent the days leading up the the event continuing his "scorched-earth campaign... ranting about a giant conspiracy involving the 'global power structure,' a nefarious media, and the Hillary Clinton campaign." 

Clinton, for her part, "will likely attack Trump for his loathsome treatment of women, as she did so effectively in the first two debates." 

So can Trump turn his spluttering campaign around tonight?  Columnist Mike Barnicle tells MSNBC that there is no way Donald Trump can do so, but if he is to make any progress, he has to "double down" on the tactics he adopted at the second debate, which were significantly better than his "weak" performance in his first meeting with Clinton, Barnicle says. 

Preamble: The third and final presidential debate in the most incredible US election campaign in recent memory is about to get underway. 

After two hostile debates, Republican candidate Donald Trump finds himself down in the polls.  In fact he is so far behind that "no candidate in the modern era of polling has climbed back from a similar deficit in October to win the presidency", notes Politico. 

But it is an election campaign unlike any other in the modern era and Trump remains defiant, insisting he can still win. 

What time and where is the debate? 

Nicknamed "Fight Night", the debate will take place at the University of Nevada, Las Vegas at 9pm ET on Wednesday 19 October (2am BST on Thursday 20 October). 

What will the format be? 

Chris Wallace of Fox News will moderate the 90-minute debate, which will be divided into six segments.  Each 15-minute segment will begin with a question from the moderator followed by two minutes for each candidate's answer and then follow-up questions from the moderator. 

What happened in the first two debates? 

Trump was largely on the offensive, interrupting Clinton and making outlandish claims. 

In the first debate, Clinton was interrupted 40 times by Vox's count, but The Atlantic says she remained "wonky, crisp, and polished; if not always inspiring".  This was "precisely the performance Clinton had wanted", adds the magazine. 

In the second, Trump attempted to deflect the furore over a leaked Access Hollywood video in which he boasts about grabbing women.  He accused Clinton of smearing women who had accused her husband of assault – something the Clintons have strongly denied.  He also said that if he were elected he would appoint a special prosecutor to investigate Clinton's email controversy, adding that she would "be in jail". 

It was a "threat more likely from a tinpot dictator than an aspirant for the highest office in the world's most powerful democracy", said Fortune. 

Should there even be a third debate? 

With Trump openly labelling the US electoral system corrupt and accusing the media of "rigging" the election in favour of Clinton, several commentators have questioned the usefulness of a third debate. 

"Let’s not allow Trump to drag down one of our most honoured processes any further," says Colbert King in the Washington Post. " For our national self-respect, pull the plug." 

QZ's Jake Flanagin writes: "Trump himself has already declared the convention as - predictably - rigged against him.  If this is the Trump campaign's official position… there doesn’t seem to be much impetus for participating". 

The US public might be starting to agree - TV viewing figures dropped by 20 per cent between the first and second debates, the New York Times reports. " Maybe Americans are starting to get fed up with the ugly tone of this strange presidential election," it adds. 

However, the second debate still drew an audience of 66.5 million and with an estimated 15 per cent of voters still undecided, the third contest could provide a crucial platform for both candidates to make their final case to the nation. 

In an election season dominated by scandals and "trash talk", there is a "hunger among voters for actual substantive debate about policy", says Darrell Delamaide at MarketWatch.  With "poll after poll showing that the biggest concern among voters is the economy and jobs", he writes, the final showdown "is the last chance to address many of these real issues one-on-one".