Donald Trump is facing a slew of claims of sexual misconduct from women
In Florida on Thursday, he fought back by strongly dismissing the accusations
First Lady Michelle Obama decried his actions as "intolerable"
Last week a video tape emerged in which Mr Trump boasted of groping women
A series of recent polls suggest a fall in his support to rival Hillary Clinton
John Beavers has been travelling around the US handing out Trump items from his custom decal Trump Truck.
"I enjoy seeing the pride of all the Americans who want the same things I want," he says.
John Beavers' Trump Truck
A hush descends and the tension is palpable, electric, as we wait for the candidates to come on stage...
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While experts analyse what to expect tonight from the candidates, the date also marks another significant moment in US presidential history. Fifty-six years ago, John F Kennedy and Richard Nixon appeared in the first-ever televised presidential debate on 26 September, 1960.
The debate is widely considered as one of the most important in election history.
More than 70 million viewers tuned to see Kennedy, a young, handsome Democratic senator, square off with Vice-President Nixon, who appeared sweaty after a recent illness.
The BBC's Franz Strasser is speaking to viewers at a bar in Seattle, while his colleague Matt Danzico is with Trump truckers in Washington state
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BBC readers from around the world have been telling us where they're watching it.
Jason Reid: "We're Brits watching from Ottawa!"
Joy Waldock: "I'm watching live in beautiful Grand Cayman."
Quote MessageI'm British from Liverpool but a student at the University of Idaho in the US. Watching the debate on campus live tonight.
Adam Jones
Andrew Watts: "Watching from Brunei!"
Quote MessageWatching the great debate live from NZ...Don't tell the boss
We've also heard from readers in the small town of Logan Lake, Canada, the US state of Michigan, Cornwall, Edinburgh, the Caribbean island of Bonaire, Khao Yai National Park, Thailand; and Dublin.
We're 15 minutes away from one of the most feverishly anticipated political cage-fights of recent years. Here's how it'll go down:
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Clinton has posted footage from the 2011 White House correspondents' dinner, when President Obama roasted the businessman for leading the so-called birther movement.
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Trump's team tells the BBC what to expect from him tonight.
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Police in Portland, Oregon, know that people watching the debate are expecting to be entertained. When the debate begins there at 18:00 local time, they'll be keeping their eye out for anyone having a little too much fun.
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The BBC's Reality Check team is on stand-by to scrutinise statements from the two candidates and highlight when they are playing fast and loose with the truth. It could be a busy night.
Some issues have come up time and again on the campaign trail, such as Trump's claim he was against the 2003 Iraq war from the start.
Buzzfeed uncovered a 2002 radio interview, external in which he supported the invasion. Mr Trump has also lobbed unfounded allegations that Clinton started the so-called Obama birther movement.
Clinton's emails could also be an issue - she has claimed in the past she "did not email any classified material".
This was contradicted by FBI chief James Comey, external. Fact-checkers have also questioned claims made by Clinton about the number of jobs her economic policies would create.
And Trump is almost certain to bring up her response to the 2012 attack on America's diplomatic compound in Benghazi, Libya.
Keep watching this page for real-time analysis of the candidates' claims as they happen.
Hours before the debate begins, campaign surrogates are already taking to the Spin Room to stump for their respective candidates.
So far we've seen Mike Pence, Donald Trump's vice presidential running mate, and Mark Cuban, the billionaire who has been a vocal opponent of Trump.
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As well as our live page, you can follow rolling coverage of the debate on BBC World News, the BBC News Channel if you’re in the UK, and the BBC World Service.
BBC announcer
The Republican nominee plays it cool as he arrives at Hofstra University.
Trump gives thumbs-up on arrival
The BBC spoke to the New York Daily News' Ginger Otis in Brooklyn on how the two candidates have prepared for tonight's showdown.
"He's going to try to go for her jugular when she tries to go for his," Otis said of Trump.
The two presidential candidates have somewhat different strategies.
Are you watching the debate outside the US? Or maybe you're in the US but watching it out with friends? Or are you following it on social media?
Tell us where in the world you're watching the first US presidential debate by emailing us at us2016@bbc.co.uk. Bonus points for photos.
Image source, EPA
Image source, Funny Or DieZach Galifianakis, who recently hosted Clinton, external on Between Two Ferns, has told the LA Times, external why Trump will never be a guest on his comedy show.
"He’s the kind of guy who likes attention - bad attention or good attention. So you’re dealing with a psychosis there that’s a little weird."
President Obama's 2014 appearance on Between Two Ferns drew over 11m viewers.
Check out what Mrs Clinton told the star of the Hangover movies.
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