Moment of truth for Hillary Clinton and Donald Trump

A cameraman is silhouetted against an an American flag during preparations for the presidential debate at Hofstra University. Photo / AP

As Hillary Clinton prepared to face the most unconventional candidate of her political career on the debate stage today, her campaign aides engaged in a deep study of Donald Trump's personality to glean insights into how he might act.

At a working group session in August, Clinton advisers met a small group hand-picked by the campaign to help shed light on the Republican nominee. The focus on Trump's personality suggests that Clinton's approach in today's first presidential debate may be quite different from her strategy in past debates - and that her campaign expects this event to be unlike any other.

The aides involved in debate prep including her aide Philippe Reines, who has played Trump in mock debate sessions. They conferred for hours with campaign outsiders who were asked to offer advice about Trump's personality and temperament.

Trump's ghostwriter Tony Schwartz, who has been one of the real estate businessman's most outspoken critics, was a part of the session. And former UBS Americas CEO Robert Wolf, a friend of President Barack Obama, also participated.

Both men - one who worked closely with Trump to write a book on deal-making and one who has himself executed hundreds of deals - were tapped to help the campaign understand how a man who has spent most of his life in the business world might behave in a debate setting.

The session represents one of the central parts of Clinton's debate preparation: to anticipate that Trump will bring an unconventional style.

Schwartz has spoken about working with Trump on The Art of the Deal. He has said that Trump's personality makes him unfit for the presidency. "He's stunningly self-absorbed and uninterested in others and he clearly has sociopathic qualities, chief important among them, a lack of conscience. And therefore he's undeterred by things that most people would be, such as telling the truth or the potentially harmful consequences of his actions."

The debate is a huge moment for the nominees, with much of the US expected to tune in amid great uncertainty about what they'll see.

The nominees are the two most unpopular presidential candidates in modern history. Both hope to discredit the other, and both hope to emerge from the debate having burnished the public's view that they are better qualified to be commander in chief.

A disagreement over the role of the debate moderator flared up yesterday, with Democrats arguing that a more activist "fact-checker" role is needed to rein in Trump's well-established pattern of factual misstatements. But Janet Brown, the executive director of the Commission on Presidential Debates, said "it's not a good idea to get the moderator into essentially serving as the Encyclopaedia Britannica". She added, however, that ultimately it will be up to Lester Holt of NBC News to do the job as he sees fit.

A new Washington Post poll shows likely voters split nationally 46 per cent for Clinton and 44 per cent for Trump, with Libertarian Party nominee Gary Johnson at 5 per cent and Green Party nominee Jill Stein at 1 per cent. An average of national polls at RealClearPolitics.com had Clinton's lead at 2.8 per cent yesterday.