His acceptance speech is likely to be a make-or-break challenge of the campaign.

Donald Trump has left himself with a mighty challenge for the final day of the Republican National Convention. After three days of tumult and controversy, the success - or not - of the week now depends even more heavily than it should on his performance today.

Trump might not have it any other way. Maybe this was always part of the plan, to create the drama and heighten the stakes ahead of his acceptance speech. After all, the campaign has always been about him. He's the candidate, chief strategist, communications director and opposition researcher all wrapped up in one unlikely package. Today, he must also be seen as a possible president.

The first days of his convention have been messy, highlighting a divided party and a convention floor that has seen angry protest and at other times what might be described as low energy. When the delegates have sparked to life, it has often been due to the contempt that many have for Hillary Clinton. The raw and unofficial battle cry here - "Lock her up!" - speaks to the coarseness and negativity of 2016.

No doubt Trump is confident about today. By his own boasts, he is the ultimate clutch performer, the man with ice water in his veins in crucial moments. He believes, as he has said throughout the campaign, that he is a winner - capable of dominating in any setting.

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What awaits him today is no Apprentice moment. It is reality TV at the highest level - as serious and critical a test as he has faced during the 13 months he has been a candidate. He'll be judged in ways he hasn't been evaluated before, and likely by a larger audience than any so far.

Ratings, however, aren't the issue. He probably will get them. He draws eyeballs, for better and for worse. But what will really count is whether Trump accomplishes everything that still needs to be done. He needs this convention to send him out of Cleveland absent controversy, without damaging questions trailing behind him and, in the best of all worlds, with a wider group of voters prepared to take a fresh look at him.

For Trump, this will be unlike the other tests of his candidacy, one that will cross-pressure him. The most unconventional of candidates now must navigate the most conventional rite of passage of any presidential campaign as he makes the official transition to general-election candidate and possible president.

Trump is at his best - and sometimes his worst - when he is mostly unscripted. His free-form style, in defiance of conventional rules of politics, worked during the primaries. But now he is being told he must curtail those instincts and use a text and a teleprompter. It will be an uncomfortable experience.

When he spoke to the Cleveland delegates from Trump Tower in New York, after being formally nominated on Wednesday, he was clearly reading his brief remarks with such cadence and precision that he conveyed his distaste at being shackled to prewritten words. But can he be both freewheeling and off the cuff, and disciplined and serious?

What's left for Trump today? Only this: He needs to energise his base. He needs to unify his party. He needs to make himself a more appealing candidate to the wider electorate. He needs to soften his image. He needs to make the case against Clinton, but more he needs to make a positive case for himself. He needs to show he has a grasp of issues and answers to problems that add heft and credibility to the slogans that have been the hallmark of his campaign.

Mostly he needs to find a way to combine the most effective theme of his candidacy - that of an outsider who connects with disgruntled and disaffected voters and will shake up Washington - with something that reassures people of his temperament, stability and reliability.

He can still redeem the week, but the opening days haven't done much to help him. As always, it's going to be all about Donald.

Winners and losers

Winners

TED CRUZ (if Trump loses):

If you like Donald Trump, you HATED Cruz's unwillingness to endorse the nominee. If you don't like Trump, Cruz took a principled stand against a candidate who he simply does not believe represents the Republican Party or the conservative movement. This speech cements Cruz as the leading anti-Trump politician in the party, the one major party leader who refused to bow to political pressure and get behind the real estate mogul. If Trump loses in November, that could well be a very good place to be.

MIKE PENCE: His speech was workmanlike and self deprecating. But, it accomplished what it needed to: Establishing Pence as a steady conservative firmly behind his running mate.

Losers

TED CRUZ (if Trump wins):

If Trump winds up being elected president - or comes very close to being elected president - Cruz effectively ended his political career yesterday. If you lose big gambles, you go bust.

PARTY UNITY: Any hopes that the story of this convention would be Republicans' ability to put aside differences was extinguished in the final five minutes of Cruz's speech. There is no papering over what happened. It was division, pure and simple. The wounds caused by the primary have not healed and may not heal.