It's time for the third and final debate of the US presidential election, and Donald Trump needs to do something radical to defeat his opponent.
The Republican nominee is still reeling from the latest set of sexual assault allegations and if Hillary Clinton wants to finish her rival off, she may seize the opportunity to humiliate him.
But it's also a chance for Trump to pinpoint his opponent's weaknesses and really twist the knife.
The 90-minute debate at the University of Nevada, Las Vegas, kicks off at 12pm AEST (9pm ET), with Fox News anchor Chris Wallace asking the questions.
It will have an identical format to the first of the three debates, consisting of six segments of approximately 15 minutes on key topics - debt and entitlements, immigration, the economy, the Supreme Court, foreign hot spots, and fitness to be president.
The candidates will have two minutes to answer each question, a chance to respond to their opponent and Wallace will use the leftover time to expand on the topic.
Both Clinton and Trump are likely to capitalise on the "fitness to be president" segment, with her doubling down on his misogynistic comments and sexual misconduct allegations. If Trump stays true to form, he will deny everything and attempt to deflect attention to Clinton's alleged cover-ups of her husband's alleged sexual assaults.
Don't give her a free pass
Trump's showmanship was partly responsible for the fact the first two debates didn't get very far beneath the surface.
O'Connor says the discussion was "really disappointing" compared to previous years, when candidates tended to "dig much deeper."
The Republican nominee could try to pin Clinton down on the foreign hot spots topic, asking what she would do differently to Barack Obama in the Middle East and what she has learnt from US interventions that have gone awry. The Democratic nominee was at the forefront of the Iraq and Syria invasions that had very negative consequences.
"It's been a bit of a free pass for Hillary," says O'Connor. "Things she's done on the record have been ignored."
Trump has already drawn attention to the fact she wholeheartedly backed the Iraq War from the very start, when he was expressing reservations - although he did appear to change his mind.
And the Republican nominee has his own weaknesses on the region, claiming he will wipe out the Islamic State, but never expressing how, or if he's willing to put troops on the ground in Northern Iraq to achieve that.
Achieving the impossible
The reality is that Trump is not in a good position right now, trailing Clinton in the polls following the highly damaging release of his lewd remarks and a series of sexual assault allegations.
"Trump needs a plausible answer to the sexual harassment claims, and I don't think he's got one," says O'Connor. "I don't think there's a winnable argument for Trump at this point, so the question is how negative he'll go.
"He's in pretty serious trouble. The allegations have been fatal to his campaign."
The third debate traditionally has fewer viewers than the first two, which have followed the decreasing pattern of 2012, with the first achieving a record-breaking 84 million viewers and the second 66.5 million.
"The key question is does it change people's voting behaviour," says O'Connor. "The cumulative effect of the first debate did change behaviour. Some sitting on the fence moved towards Clinton and that momentum was pretty strong.
"The challenge for Trump is to change some minds that have hardened against him."
Can Clinton send Trump into meltdown?
As for Clinton, she's got a history of playing it even safer than usual when she's this close to an election finish line, and being ultra-cautious and controlled.
But O'Connor warns that if she takes this too far, she risks playing into Trump's narrative that she's been tried and tested, is dull and offers nothing new.
"She needs to walk a fine line between being more aggressive than the second debate and more tactical than the first, more willing to take Trump on and get under his skin. We need to see him melt down in some way.
"In the end part of the first debate, Trump was trapped, he didn't know how to respond."
Pinning him down on the sexual assault allegations could have the same effect. "Her strongest claim is that Trump is not fit to be president," says O'Connor.
Trump has claimed previous debates have been biased towards his rival, but Clinton is likely to have the harder time in this third debate, with Wallace coming from the conservative Fox News network, whose former CEO is an adviser for the Trump campaign.
She also needs to try to appeal to younger voters who are suspicious she is part of the old system, and may still see Trump as a chance for change.