Donald Trump spent years plotting his march to Cleveland

Was it the big jet plane or the slogan that bought Trump this far? It's complicated

Even the Boeing 757 played its part in getting Trump to where he is now (Getty)

What first convinced Donald Trump to seek the presidency is only for him to know. Was it Mitt Romney failing to deprive Barack Obama of a second term in 2012? Or was his mind made up after he showed up as a guest at the 2011 White House Correspondents’ Dinner only to be mocked by Mr Obama for having spent the previous months questioning his country of birth?

“Now, I know that he’s taken some flak lately, but no one is happier, no one is prouder to put this birth certificate matter to rest than The Donald,” Mr Obama riffed. “And that’s because he can finally get back to focusing on the issues that matter – like, did we fake the moon landing? What really happened in Roswell? And where are Biggie and Tupac?” That must have hurt.

Then Seth Meyers, the comedian who was the host for the night, drove the knife in further. “Donald Trump has been saying he will run for president as a Republican – which is surprising, since I just assumed he was running as a joke,” he said to laughter at every table.

The assumption that no one need take Mr Trump and his political musings seriously was already engrained. His talents lay elsewhere: marrying, stewarding a top-rated reality TV show and running his sometimes stellar, sometimes teetering, development and casino empire. But to the political chatterati he was a buffoon and not even a very dangerous one.

What many didn’t know was that very soon after Mr Romney flopped in 2012, Mr Trump went and applied to trademark a phrase he realised at the time could be very dangerous indeed – Make America Great Again. Six days after, in fact. There is a guy selling yarmulkes bearing the slogan in Cleveland this week. He should be careful. It’s trademarked, remember.

So, it’s been on his mind for some time. But the second question we are asking this week, as thousands of Republicans flock into the city on Lake Erie to see the New York showman accept his party’s crown, is when precisely did we first begin to shed that Meyers mindset?

Some of us took longer than others to start taking him seriously. (Some still can’t.) We know now that even in the weeks after Mr Trump had declared – and smeared Mexican migrants as “rapists” and “criminals” – that the Jeb Bush campaign, based down in Miami, waited far too long.

In a podcast earlier this year, former Bush spokesperson Tim Miller, recalled arguing with media personalities in the weeks after Mr Trump's announcement about why “Trump’s a joke”. He went on: “Three months later with my tail between my legs, I called them back and said ‘All right, well I guess Trump was a real deal’.” Some people still attempt the line that Mr Trump doesn’t actually want the White House and will declare one fine day that he is pulling out.

Cleveland is getting all dressed up for the party jamboree (Getty)

Talk to his fans and a surprising number will trace their infatuation with him back to his best-selling book, The Art of the Deal, published almost 30 years ago. Some regard it as the Bible. They will not feel kindly therefore to Tony Schwartz, an author who ghost-wrote the book for the developer and who this week told The New Yorker that he regretted having done so. Mr Trump, he now wants us to know, is not a brilliant mind, he is a “sociopath”.

He pleaded guilty to “presenting Trump in a way that brought him wider attention and made him more appealing than he is,” He went on: “I genuinely believe that if Trump wins and gets the nuclear codes there is an excellent possibility it will lead to the end of civilisation. Trump only takes two positions. Either you’re a scummy loser, liar, whatever, or you’re the greatest.” He labelled him as a person with “a stunning level of superficial knowledge and plain ignorance.”

On Thursday night in the Quicken Loans Arena, Mr Trump will formally accept the Republican nomination and 120,000 red, white and blue balloons will be released from the rafters. He will wear that "aren’t-I-clever" smile (a smile that’s half pout) and his wife, who was set to headline the opening night on Monday, Melania, will join him on the stage with all his five children.

And once again half the nation and the world will ask, how the heck did he get there? How did the Republicans let this happen? If he crash-lands, or maybe even if he doesn't and wins, their party may split into two camps for good. Sulking Trumpistas – mostly white males disgruntled with their lot – will create a new, nativist, anti-immigrant, protectionist and racist "America First" movement, while everyone else will try to do what the party said had to happen after the Romney debacle. That is reach out to those people he is precisely repelling, for instance Hispanics, and get back to studying sensible immigration reform, doing trade deals and reasserting multilateralism on the world stage. If they can.

A Trump supporter scorns Hillary Clinton outside convention arena (da)

It has happened because Mr Trump knows exactly what he is doing. No accidental politician he. He understands the power of his presence and his celebrity. My moment of knowing to take him seriously came last summer when I followed him to the border with Mexico in Laredo, Texas, and his big, fancy plane landed on the tarmac, its jets roaring and his name down the side. He had an Air Force One before even starting. It gives goosebumps to people.

And that slogan tells you that even four years ago, he instinctively grasped the sourness of Republican voters towards their country, their economic prospects and their sitting president. Mr Obama, in their eyes – and of course racism plays a part – has turned America into an embarrassing and apologetic weakling, has sacrificed them to liberal, multi-cultural impulses that is taking away their jobs and their identity. (Too many immigrants, too much gay marriage.) He grasped it and then knew how to channel it.

He got other things too, for instance that bullying works as well in politics as in business. Among the rivals he dispatched: "Lyin’ Ted" Cruz, "Little Marco" Rubio and "low energy" Bush. And that exaggerations and flat-out lies aren’t going to hurt him. He knows he can shut out and ridicule the media and get away with it, mostly because his followers think it’s grand.

He and his new running mate, Mike Pence, are going to give all the miners and steelworkers their jobs back, he said on Saturday in a hotel ballroom in Manhattan. No, he isn’t, he can’t. He is going to torture not just terror suspects but families of terror suspects. No, he isn’t, he can’t. His promise to build that wall the whole length of the border is laughable. But it doesn’t matter. He can be as profane and vulgar as he pleases. Hillary Clinton right now is spending millions on TV ads re-running his most shocking statements and slanders. Will they damage him much?

So, yes, he has been bit lucky too. He boasts that he won by a “landslide” in the primaries, even though he had 15 competitors. But having so many people running helped him, because the opposition to him was split and no credible defender of the party establishment ever caught fire. Meanwhile a new study by the Harvard Kennedy School’s Shorenstein Centre on Media argues that we, the press, helped Mr Trump prevail in the primaries by simply paying far more attention to him than to his rivals, because he was a better story.

More importantly, as Mr Trump's almost certain rival, Ms Clinton is the personification of everything that so many voters are so turned off by in this election season. She is the elite. She is the untrustworthy politician. She is the establishment. She is part of the one per cent. And she is not a frightfully good campaigner either.

When does that other moment arrive, though – if it hasn’t already – when we can be certain that Mr Trump will fail in November? Did it come already on Saturday when he introduced Governor Pence as his running mate, a downer among politicians if ever there was one? No week for him is more important than this one. In Cleveland he must at same time stoke the fires of resentment and fear that bought him here and present himself as being palatable to all those other voters, including so-called independents, without whom he cannot mathematically win in November. That is what Mr Pence is meant to help with. But it will not be an easy trick.