Tonight's debate isn't until 21:00 EST (02:00 BST) - so what are the two campaigns up to until then?

President Donald Trump is holding a roundtable with supporters in Nashville at 15:00, about six hours before the debate starts in the same city.

Meanwhile, Biden's running mate Kamala Harris is taking part in "Women Mobilise for Biden" today, a virtual rally with the Women for Biden campaign group and key women leaders. Biden himself has no scheduled events as he focuses on preparing for the televised appearance.

Image source, Getty Images

The NBC News anchor and White House reporter is a respected Washington DC journalist, albeit not by President Trump who has accused her of being "a dyed-in-the-wool radical-left Democrat".

Any allegations that she would favour Joe Biden in the Nashville debate appear unfounded though.

Attacks on Welker ramped up after a New York Post article citing her parents' history of donating to Democratic politicians, and attacking the journalist's "scathing style of questioning", external.

But many of her peers have been quick to defend Welker.

Even senior Trump adviser Jason Miller described her as "very good choice" in a recent interview with Fox News

“Look, I think I have a very high opinion of Kristen Welker,” Miller said. “I think she’s going to do an excellent job as the moderator for the third debate. I think she’s a journalist who is very fair in her approach."

Aged 44, Welker is the youngest moderator of this year's series of debates, and how she handles what - despite new debate procedures - is likely to be a combustible encounter, will be closely watched and much commented on.

Olga Robinson
BBC anti-disinformation unit

US national security officials say Iran was responsible for sending threatening emails to Democratic voters in several states, urging them to vote for President Trump - or else.

But what did those targeted make of the emails, which were made to look like they came from a far-right pro-Trump group?

A few voters who have been speaking to the media – mostly on condition of anonymity – said they had been initially confused by the threatening message, but quickly dismissed it as a joke or scam.

Some said they had reported the email to Google, while others tweeted they had notified the authorities about it.

But not everyone has been unaffected. One female voter told CBS News that although she personally had not been intimidated by the email, her elderly mother was.

Google says about 25,000 emails have been sent to users of its mailing service, but some 90% of those were blocked by its spam filters.

Here’s how you can spot the hallmarks of foreign and domestic influence campaigns on your social media feed and your inbox:

President Trump and his predecessor, former President Barack Obama, have mocked each other at rival rallies.

Speaking to a crowd in Gastonia, North Carolina, Trump made fun of Obama for being wrong about the outcome of the 2016 election.

"There was nobody that campaigned harder for crooked Hillary Clinton than Obama, right?" he said. "I think the only one more unhappy than crooked Hillary that night was Barack Hussein Obama."

At the same time, Obama - who is campaigning in support of Joe Biden, his Democratic vice-president - told voters in Philadelphia that voters wouldn't tolerate the kind of conduct they see from Trump, "except for maybe a crazy uncle somewhere".

"Why are folks making excuses for that?" he said. "Oh, well that's just, that's just him. No, it's… no! There are consequences to these actions. They embolden other people to be cruel. And divisive. And racist. And it frays the fabric of our society."

Image source, Reuters

Unexpected entry? Perhaps. We know tonight's debate had national security as one of the 15-minute fragments, but no-one might have expected to be given such a shocker of a headline barely 24 hours before the contenders take to the stage. It came by none other than National Intelligence Director John Ratcliffe.

Iran and Russia, he warned, had obtained US voter registration information and used it to influence and intimidate voters.

In one instance, Iran posed as the far-right Proud Boys group and sent threatening emails to Democrat supporters, Ratcliffe said. The emails were meant to "incite unrest".

However Russia and Iran both deny the accusations. Iran's foreign ministry spokesman, Saeed Khatibzadeh, told state TV that the claims were "repetitive, baseless and false".

Kremlin spokesman Dmitry Peskov told the BBC: "We think this is unfortunate. These accusations come every day, they are all completely groundless, they are based on nothing."

Read the full story here

The debate will be held at Belmont University in Nashville, Tennessee, and you can follow it live on this website.

The 90-minute encounter will be divided into six 15-minute segments, with each candidate given two uninterrupted minutes before they engage each other. Here comes the important difference from the first debate, which was filled with interruptions: during these two-minute blocks, only the candidate who has the floor will have his microphone turned on - the other will be temporarily muted. Let's see how well that works out.

The six segments will address six separate topics:

• Fighting Covid-19
• American Families
• Race in America
• Climate Change
• National Security
• Leadership

And in terms of coronavirus, safety protocols are expected to be similar to the first Trump-Biden face-off. Candidates will be spaced a safe distance apart and they will not shake hands.

Image source, Reuters

Good morning from our reporting team in Washington DC and London.

A lot is happening today. To help you catch up, here are the latest headlines.

• Tonight, President Donald Trump and his Democratic challenger Joe Biden go head-to-head in their final debate of the election campaign. It’s kicking off in Nashville, Tennessee, at 21:00 EST (02:00 BST, 01:00 GMT)
• The last time the two candidates went up against each other, it descended into an unintelligible squabble; this time organisers say they’re introducing mute buttons, so Biden and Trump can both deliver their opening statements without interruption from the other
• With record unemployment and civil discord over racism in the US, there’ll be no shortage of topics - but the overarching issue will be the coronavirus pandemic
• This is the first debate since Trump himself was admitted to hospital with Covid-19 at the start of the month. A debate that was scheduled after that was cancelled after Trump refused to take part virtually
• Meanwhile the US still has the highest total number of cases of coronavirus, with more than 8.3m infections, and the highest death toll in the world, of more than 220,000
• The FBI says that Iran and Russia have been using US voter registration information to try and interfere in the election
• Among the examples given by Director of National Intelligence John Ratcliffe was an instance of Iran posing as the far-right group Proud Boys to send intimidating emails to voters
• A key committee vote is being held today to confirm the nomination of Amy Coney Barrett to the Supreme Court - but Democrats are threatening a boycott, in protest against what they say is the rushing through of a replacement for Justice Ruth Bader Ginsburg, who died last month.