Within minutes of the start of yesterday’s proceedings of the Chilcot inquiry, a tanned Tony Blair gave us the key to understanding his motivation. But it took the whole day’s grilling, right through to his final, defiant Je ne regrette rien, for me to solve a bigger puzzle: our own motivation. Why the national and media infatuation with making this man squirm?

First, to what makes Mr Blair tick. How many viewers, watching the inquiry yesterday, noted his answer to a very early question? He rolled together in a single two-word phrase two political groupings in the Middle East who were in fact bitterly opposed to each other: “these people” was his collective term for Baathist nationalism and internationalist Islamic fundamentalism.

Worlds apart, surely? Forgive the italicisation, but this cannot be overemphasised: Tony Blair believes that all bad people are on the same side.

The key to explaining this man, and to understanding his genuine fellow-feeling with the former President George W. Bush and with the mindset of the American Right, is his religious outlook. Until you recognise that Mr Blair really does do God — and recognise the way in which he does God — you will miss the philosophical mainspring.

I was, to my shock, confronted with this recently when by chance I encountered Mr Blair outside Westminster Cathedral, where he had been queueing to touch a casket containing the touring bones of a Roman Catholic saint. I was reminded of it again yesterday when, for all his slipperiness in avoiding difficult questions from the Chilcot committee, I got the strongest of impressions that Mr Blair was utterly sincere about the decisions he took on Iraq.

He was asked why, in 2002, his attitude changed to the already well-known risk posed by Saddam Hussein, even though the facts remained the same.

“After September 11,” Blair replied, “I realised we could not take risks with these people at all.” These people. Which people? But Tony Blair does not confuse them. He acknowledges (he did later) that Saddam had no links with al-Qaeda.

Mr Blair does distinguish the many and various dangerous forces around the globe. He distinguishes them but he sees no difference between them.

This was evident later when he was asked about other threats, his questioner citing Yemen, North Korea, Afghanistan and Iran. “I’m afraid,” Blair replied “my view is that they’re all part of one picture.”

Tony Blair is a Manichean, or dualist. He believes that the Universe is best understood as an eternal struggle between the forces of good and evil, in contention for dominance. Christians are supposed to believe that the battle is already won, and Mr Blair’s dualism is (paradoxically) closer to Islamic fundamentalism than to the Gospels. For Mr Blair at least “Axis of Evil” was not just a Bushite soundbite: it was a profound philosophical insight into the meaning of world history. Once you understand this, there is no arguing with him.

But as I watched Mr Blair an unfamiliar feeling stole over me. Sympathy. Here was a team of pre-eminently Establishment figures, prodding and needling and raising the occasional eyebrow in discreet incredulity. And all — make no mistake — for a simple reason. Because the war on Iraq turned out badly.

Imagine (I thought) that those weapons of mass destruction had in fact been found. Would we be quibbling about whether the evidence beforehand had been sexed up? Imagine that after the toppling of Saddam a grateful Iraqi nation has linked arms to establish a happy and united democracy.

Would we now be picking over the legal precedents and finer points of international law? Would we be agonising over whether the Attorney-General was or wasn’t arm-twisted into giving that final green light, if the green light had led, in the end, to success? The dubious legal basis for the Iraq occupation was not the reason it went wrong; nor was the failure to find WMDs. And many’s the capricious and hastily planned adventure that nevertheless yields a happy outcome.

When Mr Blair remarked, rather wistfully, yesterday: “It all depends on what happens afterwards as to how people regard your behaviour at the time,” he was surely right.

What will doom Mr Blair’s personal legacy is the lethal confluence of two very different tendencies in British opinion. The first, of course, is those millions who opposed the invasion from before the start — many of us making it clear we would think it a mistake even if it succeeded in its aims. Among us there’s an appetite for rubbing his face in the failures of the mission. We’d be happy to stage one of these inquiries every five years (say) — like a traditional morality play, school Nativity play or pantomime, where the plot and the dramatis personae remain familiar and unchanging, and the audience knows when to boo.

But in recent years a second and, for Mr Blair, more ominous grouping has joined the critical chorus: those who supported the invasion and now feel they have been made fools of by events. They include many instinctive neoconservatives who have been bruised by the disrepute into which the adventure has fallen. They include, too, a range of media commentators and democratic politicians (including many senior Tories) who are embarrassed by positions they once took and feel, perhaps unconsciously, that they’ve got some explaining to do.

They include, most ominously of all, a number who have not really repented of their doctrine of muscular interventionism, are now eyeing up Iran, and badly need to distinguish between what happened last time and what might happen if we try it again.

This brigade of hindsight-doubters share an interest in blaming Mr Blair and Mr Bush personally for their conduct of the mission. The brigade’s unspoken refrain is that there was nothing wrong with the idea (that’s why they supported it) but everything wrong with the bungled execution.

That they have now turned on Tony Blair dooms his legacy in a way that the bleatings of peaceniks like me never could.

And so, as former friends desert, our former leader heads off into the wilderness, a scapegoat burdened down with the consequences of what was, in truth, a bad idea — not a good idea badly executed. Mr Blair will spend the rest of his life (as someone once said of Edward VIII) growing more and more tanned, and more and more tired. Yesterday, and for the first time, I almost pitied him.