Tonight is the final debate of the election campaign, ahead of polling day on 3 November.

A lot is at stake. For Trump, it's a chance to turn around his campaign, given he has been trailing in the polls. Meanwhile, Biden will work to maintain his frontrunner status, hoping to avoid any stumbles.

And after the last debate - which descended into chaos - organisers are introducing a mute function, so that both candidates are able to deliver their opening statements uninterrupted.

Here's what else you need to know.

When is it happening: The debate will start at 21:00 ET (02:00 BST) and will end 90 minutes later.

Where is it taking place: It's being held at Belmont University in Nashville, Tennessee - but you can follow it live on this page.

What's being discussed: The debate will be separated into six segments, each covering a different topic. These are: Fighting Covid-19, American Families, Race in America, Climate Change, National Security, and Leadership.

Image source, Getty Images

Trump is currently ahead in the polls in Texas - but could a Seinfeld-themed fundraiser swing things in Biden's favour?

Julia Louis-Dreyfus and Jason Alexander - who played Elaine Benes and George Costanza in the iconic "show about nothing" - are holding the virtual fundraiser with Seinfeld co-creator Larry David tomorrow night, to try and get the state to vote blue.

They're calling it "A Fundraiser About Something".

They're not the first celebrities to endorse Biden. Earlier this month, our reporter Holly Honderich took a look at some of the stars voicing their support for the Democrats.

The president has tested negative for Covid-19 ahead of tonight's debates, according to his chief of staff, Mark Meadows.

This follows an announcement by the Biden campaign that the former vice president was also free of the virus.

Marianna Spring
Specialist disinformation and social media reporter

What kind of rumours and murky stories will feature tonight?

Top of the list must be a controversial New York Post article containing claims about influence peddling and Joe Biden’s son Hunter. Will President Trump bring the story up? Maybe a better question is: behind as he is in the polls, how can he resist?

And on social media, there are even more malicious rumours circulating. Expect fireworks if those get an outing.

Another story of the moment is the threatening emails sent to voters, purporting to be from the pro-Trump Proud Boys. The FBI says that Iran was behind them. At one time this debate was supposed to be about foreign policy, so we’ll see if that issue slips into the running order.

And no matter what the candidates say, expect social media to be filled with now-familiar (and widely debunked claims) – about secret ear pieces, and about postal voting.

And how can you spot disinformation on your social media tonight? Here are some top tips.

Donald Trump campaigned for the presidency in 2016 with a pledge to bring down illegal immigration.

At the time, he famously blamed undocumented migrants from Mexico for a host of problems in the US - including drugs and crime.

So, in four years of a Trump presidency, how has immigration in the US changed?

We've mapped out some of the stats - and you can read more about immigration under Trump here.

Laura Trevelyan
BBC World News America presenter, Nashville, Tennessee

The president has just landed here in Nashville on Air Force One and he’s on his way to Belmont University for his walk through the debate stage.

Then he’s off to a big donor fundraiser where he and his daughter Ivanka are speaking to deep-pocketed supporters at the JW Marriott hotel downtown - back here for the debate.

This is the scene outside the debate hall.

Trump departing for the debate from the White House, accompanied by his wife Melania.

Image source, EPA

Last month, North Carolina's State Board of Elections announced that absentee ballots could be counted until 12 November, as long as they were postmarked 3 November or earlier.

Now, the Trump campaign is asking the Supreme Court to shorten the state's deadline, arguing that it could lead to unequal treatment of voters.

The change was made as part of a settlement with a union-affiliated group, which argued the deadline needed to be extended to account for possible postal delays.

The state board has a Democratic majority, but the settlement was approved by two Republican board members. They later resigned after backlash from their party.

North Carolina voted for Trump in 2016 - but according to the most recent polling, Biden currently has a slim lead in the state.

We're watching tonight's debate with voters from battleground states - the places that will ultimately decide the election.

First up, meet Noel Brown. He's a dual UK-US citizen and undecided voter. He prefers Biden as a person but is more supportive of Trump's policies.

What are you looking for in the final presidential debate?

A more reasonable exchange of policies and to learn what impact the next four years will have on the USA. The votes of the undecideds and independents are at stake tonight.

Why are you undecided?

I like the Trump administration's policies but feel he is not respectful of the office of the President of the United States. I do not like that Biden has been hiding in the shadows and wonder if he has a hidden agenda. I have not voted yet, I plan to vote on 3 November in person.

Noel is a member of our US election voter panel. We want to hear from you - what questions do you have for our focus group tonight?

It would seem not even standing in torrential rain without a coat or umbrella is putting people off from casting their vote in the US state of Florida.

Voter Lawrence Bryant posted this video of a queue in Ocoee, Orange County, on Wednesday, and told the BBC that for half of his hour-long wait to vote the heavens opened.

"I just want folks to see how important this election is," he said of his reasons to post the video.

Early in-person voting began in the battleground state this week ahead of 3 November election.

The pandemic. Healthcare access. Race. Women's rights. The environment.

These are some of the biggest issues of the upcoming election - so where do Trump and Biden stand?

Read our guide to each candidate's views.

Image source, Getty Images

The US Postal Service has delivered over 100m blank or completed mail-in ballots since the beginning of September, according to a press statement. In total, USPS says, 523m pieces of election mail have been processed - "162% more than during the 2016 election", external.

It's yet another indicator of how voting habits are changing and enthusiasm seems high even in the midst of the pandemic. According to the Washington Post, external, 42.1m people have already voted, which puts the country on track to surpass the amount of early voting in 2016. That's good news for the Democrats, who outnumber Republicans 2 to 1 in terms of early voting.

However, it's also true that more Republicans report they will vote in person on election day, which conservatives hope will overwhelm this early showing by Democrats.

Thanks for tuning in today - let’s chat for a moment!

We know this political circus can get complicated - that’s why we’re here. If you’ve got questions about the US election, BBC journalists across the US want to answer them.

Submit your questionshere.

And you can check out some election questions we've already answered here:

• Your top questions answered
• What is the electoral college?
• How Trump and Biden compare on abortion
• What do young Republicans think of Trump?

Image source, Getty Images

Jennifer Lawrence says she grew up Republican, and voted for John McCain over Barack Obama - before voting for the Democrats in subsequent elections.

"I was fortunate to grow up in a Republican house, where I could see the fiscal benefits of some of the Republican policies," she told Heather McMahon on the Absolutely Not podcast., external

"But then, for me, when Donald Trump got elected, that just changed everything."

She's joined by Republican Senator Mitt Romney, a former presidential candidate himself, who also recently revealed he did not vote for Donald Trump.

Also on The Countdown, our reporters Tara McKelvey and Anthony Zurcher have put together an alternative viewing guide to tonight's debate, while we take a closer look at Trump tweeting out his interview with CBS's 60 Minutes in full.

Read more here.

Robin Levinson King, BBC News

Ladara, 30, from Seattle, Washington, asks: Why is it more difficult to vote this election?

The pandemic has made voting extra difficult this year. There are obvious health risks to crowding together at a polling station, so many states have expanded early voting, either in person or by mail.

But each state has its own rules and regulations about who is allowed to vote early, and how it should be done. In Pennsylvania, ballots must be “clothed” in a privacy envelope. In South Carolina, a witness must verify your ballot.

There are currently over 300 lawsuits in 44 states concerning how absentee votes are counted, who is allowed to vote early and how mail-in ballots are collected.

All these changes and legal battles can make things really confusing to the voter, and exacerbate long-standing issues, like long queues and long drives.

Read more on this issue here.

Do you have a question about the US presidential election that you would like our team to answer? If so, submit your question here.

Image source, Reuters

We reported earlier that the FBI said Iran and Russia had used US voter registration data to target Democrats - in some cases posing as far-right groups to send intimidating or threatening emails.

Now, Speaker of the House Nancy Pelosi has said that while Iran is a "bad actor", it is "in no way equivalent" to Russia.

"Everything that we've seen here in the public domain does not justify the statements that we heard yesterday," Pelosi said, before a classified briefing with intelligence officials.

"Russia is the villain here. From what we've seen in the public domain, Iran is a bad actor, but in no way equivalent."

We're watching tonight's debate with voters from battleground states - the places that will ultimately decide the election.

Next up, Jessica. Joe Biden was not her first choice in the US primaries but she will cast her vote for the former vice-president because she likes and respects him a lot. An attorney and self-described 'news junkie', Jessica admits to feeling exhausted by this election.

What are you looking for in the final presidential debate?

I'm looking to see a side-by-side comparison of the candidates. This was nearly impossible during the last debate because of Donald Trump constantly interrupting Joe Biden. I want to be able to hear Joe Biden articulate a full response without interruption. Tonight is the final opportunity to change minds.

Why do you support your candidate?

I support Joe Biden because he's a good and decent person who has experienced the struggles of regular everyday Americans. I think he's in politics for the right reasons, and is running for president to restore and advance the ideals of this country, not for personal gain or hubris. More concretely, he'll enter us back into the Paris Climate Accord.

Jessica is a member of our US election voter panel. We want to hear from you - what questions do you have for our focus group tonight?

Donald Trump has taken the "unprecedented decision" to release footage of his interview with CBS's 60 Minutes programme - decrying the "bias, hatred and rudeness" shown towards him.

The president has complained for days about his treatment during the interview. The footage released shows a staff member off-camera saying there are five minutes left in the interview, before Trump says "I think we have enough of an interview here, that's enough".

Stahl had pressed the president on the economy, the pandemic, and his plans for healthcare.

CBS, which was due to broadcast the interview this weekend, said in a statement that the White House's "unprecedented decision to disregard their agreement... will not deter 60 Minutes from providing its full, fair and contextual reporting which presidents have participated in for decades".

Image source, Getty Images

Image source, Photo by Drew Angerer/Getty Images

Dr Moncef Slaoui, the chief adviser to President Trump's vaccine task force Operation Warp Speed, predicted that a vaccine could be widely available by spring of 2021, and that by June of that year, all Americans could be vaccinated.

"We can start immunising the highest risk people, front-line workers, the healthcare workers, before the end of the year," Slaoui said in an interview with ABC News., external

That timeline goes counter to his boss'. In his first video message after leaving Walter Reed Hospital, Trump repeated his prediction that a vaccine could be available before or immediately after the election - although he has also said in the past that a vaccine would be available by April 2021, external.

Dr Slaoui, the former head of vaccines at GlaxoSmithKline, said that he has experienced no political pressure to fast-track the vaccine, and that if he were asked to do so, he would resign. He also expressed concern that nearly half of Americans polled said they would not get the vaccine if it were available today, external.

"I'm really worried about that," he said. "I think, unfortunately, it's the politics around it."

The Trump campaign is relying heavily on the president's daughter, Ivanka, in its last-minute bid to win the votes of white, college-educated women.

According to Politico, external, Ivanka Trump has made 17 campaign stops in the last six weeks in battleground states like Pennsylvania, Florida and Arizona. Her strategy is to personalise the president, and hit more moderate talking points about her work on paid leave, school choice and human trafficking.

Suburban women helped propel Trump to victory in 2016, but some polls now show that rival Joe Biden is winning this crucial demographic by as many as 20 points.

This fact does not seem lost on the president, who remarked at a recent rally, external, "Can I ask you to do me a favour, suburban women? Will you please like me?" - though Trump says it's meant to be taken in a joking manner.

Image source, Reuters

Jiyar Gol
BBC Persian

Image source, Getty Images

The Iranian government would most definitely love to see a president Biden in the White House rather than President Trump next year. Since the US pulled out of the nuclear deal two years ago and re-imposed sanctions, the Iranian economy has been on the verge of collapse.

The spoof emails could be the work of hard-line elements within the Iranian regime, close to the Revolutionary Guards (IRGC). They don’t care who is US president and - watching President Trump cast doubt on the upcoming election result – are likely to want to see more division, chaos and doubts over US democracy.

In recent years, the IRGC and the ministry of intelligence have rapidly improved their cyber warfare capabilities. This is particularly true of the IRGC who are not in line with Iranian government policy most of the time. They might be trying to add fuel to the divisions in Trump’s America.