With just a few days until the Iowa caucus, the Republican candidates want to spend their time talking about themselves. They want to lay out their policies and plans, point out how they'll be better than President Obama, and how they are the best candidate in the race.

They don't want to spend their time talking about someone else.

But here in Iowa, that's all they've been doing all day. And yet again, it's Donald Trump dominating the conversation.

He has decided that he won't take part in the final Republican debate on Thursday before the Iowa caucuses, the first public test of the candidates' electability.

He is upset with the organisers, American cable channel Fox News. He doesn't like one of the moderators, thinks she has been mean to him in the past, and so he has decided to take a pass.

It's a stunning step. At first it looks petulant and childish, but it is so much more than that.

Let's try to pull it apart.

Trump has run his campaign to his own rules. Things that people have thought would hurt the candidate simply haven't. He has called Iowa voters "stupid", attacked US prisoners of war, and made claims that have been proven to be untrue. Yet his popularity continues to rise.

Trump is backed by former vice-presidential candidate Sarah Palin [Mary Altaffer/AP]

'Not a politician'

He insists he is not a politician, not part of the establishment, and is the face that - in the words of his campaign - will make "America great again".

Fox News has a right-wing tilt. It is where Republican candidates get most air time in front of an audience that is hugely sympathetic. Its Republican debates have brought in record ratings.

Some people might consider that ducking out of the debate will hurt him. There is a feeling that Republicans can't cross Fox without being punished. But Trump can now claim that the channel is simply part of the establishment that he is running against. 

Incredibly for a channel that has spent years telling its audience that there is a media bias against the right, Trump has turned that against them, telling his supporters the channel can't be trusted to act fairly.

 

And incredibly for a channel that has spent years telling its audience that there is a media bias against the right, Trump has turned that against them, telling his supporters Fox can't be trusted to act fairly.

And so he is hosting his own event here in Des Moines, and it is certain to be covered live on every cable news channel that is not Fox.

But let's turn to the debate.

While Trump has got better in the six previous debates, he still struggles to expand his policies beyond the soundbites and statements. He looks uncomfortable. To paraphrase one Republican consultant, he's looked like a school kid winging a report he should have prepared before standing in front of the class.

And if he had taken the stage he would have faced some really tough questions from the moderators and, as the frontrunner, his fellow candidates. That may have exposed him more than he wants or needs at this stage of the race.

Many of his supporters seem concerned that he won't be there but his non-appearance might actually work to his advantage.

His closest rival, Ted Cruz, now will be the frontrunner on the stage.

He looked rattled by some of the exchanges in the debate two weeks ago in South Carolina, and Cruz will now become the focus of attacks from other candidates.

If he performs badly, all that will do is strengthen Trump. If he performs well, Trump can say Cruz did well because he wasn't there. If ratings are down, Trump will claim it's because he was absent.

Trump has re-written the book on how to run a presidential campaign. It works for him because of his unique personality - and it's working in the polls.

The Republican Party won't speak out against him. It is worried about attracting his anger, turning his supporters against it, or, in the worst-case scenario, forcing Trump into an independent third-party run that would virtually guarantee a Democratic win in November.

There may be some who don't want a prospective commander-in-chief taking actions because of emotion.

But though Trump won't be on the stage, this latest Republican debate will be all about him.

What does Palin's backing mean for Trump and the US?