As much as you may like to see it as a vanity project, the humiliation awaiting him (if his many critics were right) would have far outweighed his desire to be front and centre, and if he hadn't done the homework, seen a few numbers, worked out a realistic challenge, you never would have heard from him.
Do remember he's talked for years about running but never did.
Why now?
Because he's smart and he saw the gap, he saw what Bernie Sanders saw. America politically is broken, and people are sick of it. He also has what many Americans love ... success.
You must never underestimate an American's desire to be successful, either personally, nationally or globally.
Which in part brings us to a subtheme of the main theme: Obama gave us Trump.
Obama has one great thing going for him that can never be taken away, he was that country's first black President, and when you look back at the tape of those glory days on the night of the first victory in 2008, all things seemed possible. And in reality, so little of that promise was ever delivered on.
Obama lost any authority in Congress by 2010, the mid-terms delivered defeat and the Republicans have been winning ever since.
Obama is a lame-duck President who has done and can do very little before he shuffles off this coming January. And in that political malaise has grown a disenchantment, a belief that what America is capable of hasn't or isn't being realised.
So along comes Trump with the simplest of messages: We can make America great again.
Ronald Reagan had the same trick ... the shining city upon a hill.
Americans want to be great, and Trump is telling them they can be.
Not only has America moved significantly to the centre right in Congress, the White House has been occupied by a Democrat for two terms ... and not just that but a liberal Democrat.
Between the two terms of a liberal Democrat, the shifting to the right of Congress and - our third theme - the baggage of Hillary Clinton, you can mount a very strong argument that the White House in 2016 is the Republicans' to lose.
It's just a question of which Republican is going to do it.
What may well prevent it being Trump is if the Republican establishment, who hate him and rightly fear him, could get their act together and work out a single player to run against him.
As impressive as his win in New Hampshire was, the field was being split at least four times over.
Between Cruz, Rubio, Kasich and Bush, they're making it easier for him that it ever should've been.
Personally, my establishment figure is Rubio. He's young, which is important for a party that produced a seemingly neverending string of old blokes in beige pants and blue blazers, and he would play well against Clinton given she's old.
Further, he's bright and can match her in any category including her strength of foreign relations.
He has a magnificent back story, being the son of immigrants who arrived with nothing.
But none of that matters if they can't agree that all four of them continuing is going to do nothing but send Trump all the way to the nomination and potentially the presidency.
If things keep going the way they are, this race might be over in a couple of weeks.
At the beginning of March we have Super Tuesday. There are hundreds of delegates up for grabs that day, and having won New Hampshire so convincingly and, short of disaster, winning South Carolina this weekend, it is entirely possible the Trump train will have so much momentum it will become unstoppable.
So to the Democrats.
Although Sanders has the same outsider credentials Trump has, he won't win.
Why? Because he's old and mad.
The Democratic field ironically has suffered from lack of numbers. Hillary, although in a way tougher battle than I'm sure she ever thought possible, will prevail because she has money and experience. As much as Sanders has ignited the young and trendies who are as sick of the establishment as Trump's Republican supporters, the difference is Sanders isn't electable. You may fairly argue neither is Trump, but he's more electable than Bernie because he's his own man, answerable to no one, and has all the money you need to win.
Unless Michael Bloomberg enters.
Don't rule that out. The very reasons that saw Trump and Sanders enter and do so well are still ripe for a third - dare I suggest - more sensible player.
According to Frank Luntz, a pollster freakily good with numbers, if Bloomberg enters he starts with an automatic 25 per cent - and he too has the money to win. Luntz says at that point all bets are off.
What makes this so gripping is it's gone beyond the circus it started out as, with the Trump detractors chortling over his folly. He may well end up President of the most powerful nation on earth. And if that hasn't got your attention, nothing will.
