What folly. What crass, indescribable, unbelievable folly it was to invade Iraq in 2003. I wonder what George Bush, Donald Rumsfeld and Tony Blair think now as they read of the latest disasters to befall that wretched land.
Do they still say that Iraq is better off than it was under Saddam Hussein? Do they? Really? As half a million terrified people flee from their homes to escape a jihadi group so extreme that even al-Qaeda has withdrawn its backing?
Guess, by the way, who said this, referring to their support for the invasion in 2003: "I thought I had acted in good faith and made the best decision I could with the information I had. And I wasn't alone in getting it wrong. But I still got it wrong. Plain and simple."
It wasn't Bush, Rumsfeld, or Blair - but you knew that. It was Hillary Clinton, in her just published memoirs, clearing the decks for a run at the US presidency in 2016. Even if it is carefully-calibrated political positioning, I can't help wishing more leaders would say something similar.
The invasion of Iraq may well turn out to have been the most disastrous military adventure since the German army marched into Poland in 1939 and triggered the Second World War. Did Hitler still believe, as he prepared to die in his bunker in 1945, that invading Poland had been a good idea? Was he as crazily delusional as Bush, Rumsfeld and Blair?
Perhaps, despite the lightning advance of the Sunni jihadi fighters over the past week, Iraq will somehow survive. Perhaps not. Perhaps it's about to join such unhappy nations as Somalia, Syria and Libya as yet another failed state, ruled by a nightmare patchwork of brutal militias, loyal to no one but their own commanders and with no interests other than those that are narrow, sectarian and tribal.
In 2003, there was no al-Qaeda presence in Iraq. Now one of its nastiest off-shoots controls vast swathes of the north and west of the country, extending across the border into Syria as it starts to build its trans-national Caliphate. It's not exactly what the US-led invasion was designed to achieve.
In the pantheon of those to blame for all this we must include Nouri al-Maliki, the Iraqi prime minister whose incompetence, corruption and Shia sectarianism has encouraged the country's Sunni minority to join, or at least acquiesce in, the jihadi insurgency. It seems even Saddam loyalists from the former Ba'ath party have joined them - how's that for irony? With a different man at the helm as the US pulled out the last of its troops, it's just possible that disaster could have been averted. But it was not to be.
What has happened has happened. The Kurds in the north are buttressing their defences; their forces are ready to fight back if the Sunni Arab insurgents dare to threaten their hard-won autonomy. The Iraqi army appears to be disintegrating - so much for the countless billions of dollars spent on training a new national force.
In its place, various Shia militia groups are forming, or re-forming, to defend what they regard as essential Shia interests, including the Shia shrine in the mainy Sunni city of Samarra. The shadow of a renewed civil war looms frighteningly large.
In the words of the US Republican senator Lindsey Graham, after having been briefed by the Pentagon on Thursday: "What I heard today scared the hell out of me. The briefing was chilling ... Iraq is falling apart."
And it's not only the fate of Iraq that is at stake: the regional ramifications are seriously worrying. To the west and to the east, in Syria and Iran, the latest developments will be causing deep anxiety. President Assad will be watching with alarm as the insurgents snatch arms and ammunition from abandoned Iraqi army armouries and start shipping them across the border into Syria. And in Tehran, they'll be less than thrilled to see their Shia allies in Baghdad under threat.
So there's a strong possibility of even more bad-neighbourly intervention, never forgetting Turkey's nervousness at any sign that the Kurds may be consolidating their claim to statehood. (Strange, isn't it, how the US and Iran find themselves on the same side as the main backers of al-Maliki?)
This is a deeply uncertain time, but there is one certainty: neither the US nor the UK, which did so much to unleash the forces that are now destroying Iraq, will send their own troops back in again. Good thing, too: Western military intervention would simply make an already terrible situation even worse. And that includes the drone strikes that president Obama is reported to be contemplating - they haven't exactly done wonders for pacifying either Pakistan or Yemen, have they?
What the West can do - should do - is arrange urgent help for the civilians whose lives are being destroyed. And once the picture is a little bit clearer, they might try to encourage neutral mediators like Norway or Sweden to start a talks process aimed at turning the clock back to post-invasion 2003 and charting a new constitutional course for Iraq.
I fear it may already be too late. I've just looked at the diary I kept during the 2003 invasion; the last entry, written after the fall of Baghdad, reads: "I think Iraq is going to be a violent, messy, angry place for a long time ... I'll probably be talking about Iraq until I retire."
I should have added one more line: "And beyond."