Here in Baghdad, it's beginning to feel like a critical moment.
In the last week this city has seen 22 car bombs, with 10 on a single day - last Friday. Not far from Baghdad, at Musayyib, between Hilla and Karbala, nearly 100 Shia Muslims were killed.
A tanker bomb killed nearly 100 people in Musayyib
The shadowy resistance movements seem to be operating on a new and much more ambitious level.
Last summer, and in the summer of 2003, there were similar peaks, though much lower ones: The ferocious heat seems to produce new reserves of anger and violence here.
As I flew in, sitting in the aircraft cockpit, Baghdad lay dark and irregular, like a blotch of ink, straight ahead of us. Below lay the ribbon of road from the south.
In the months after the US-led invasion of Iraq we used to drive up that road to get to Baghdad. By the beginning of 2004 that was already becoming much too dangerous, and we had to fly.
The pilots looked at each other, and the plane went into a fierce dive, down towards the military airfield on the south-west of the ink-blotch.
We straightened out, then banked so steeply to the left that everything loose skidded across the cockpit floor. Then a sudden turn, equally heart-wrenching, in the other direction.
During the hour-long flight the pilots scarcely spoke to me. Ever since an RAF Hercules went down north of Baghdad, six months ago, air crews have concentrated totally on the job of getting their planes in safely.
The plane door opened, and we clambered out. The air was as hot as an electric heater: 50C, even in the late afternoon.
The sun glared down angrily through the haze, reddish and inflamed like a nasty wound.
On average as many people are now dying here every day as were killed in the London bombings
Ahead of us lay the most dangerous stretch of road in the world: the highway from Baghdad to the airport. Two car bombs had just been discovered along it.
Another change since I was last here, a few months ago: the Iraqi national police were out in force along the road, stopping cars of particular makes, and particular colours; that's how they found the two car bombs before they went off.
Yet the greater numbers of police haven't stopped the bombers; on the contrary, they have given the bombers a new target - the police checkpoints themselves.
I visit Baghdad at least four times a year, to see how things are developing. Since the fall of Saddam in May 2003, and the capture of Baghdad, after which major operations were declared over, I have been here eleven times.
Each time the security situation has been markedly worse than the time before.
Briefly, after the election in January, which brought an Iraqi government to power, things seemed to improve; then, after some weeks of fewer bombs and fewer deaths, the level of attacks rose again.
Now it is higher than it has been at any time since May 2003. The supply of suicide bombers seems endless.
Two separate campaigns appear to be going on: the Baathist resistance movement which Saddam Hussein planned and provided vast stocks of weapons and money for, is targeting the Iraqi army and police, and to a lesser extent the American and British forces.
Iraqi checkpoints have become targets for bombers
As far as anyone can tell, this is the larger and better equipped of the two main underground movements.
The other is the extremist religious movement headed (we assume) by Abu Musab al-Zarqawi, which announced last year that it was associating itself with al-Qaeda. Foreign Muslims in sizeable numbers have come into the country to support it.
Intelligence officials in Baghdad say this group gives the appearance of being more active, because it apparently has a policy of claiming responsibility for major attacks whether or not it has actually carried them out.
But to be honest, who does what is largely a matter of guesswork.
Someone, though, is deliberately targeting Shia Muslims. Last Friday's attack in Musayyib was carried out by a suicide bomber driving a hijacked petrol tanker. It exploded outside the Shia mosque.
Both of the main streams of resistance, the Baathists and the supporters of al-Qaeda, are predominantly Sunni, and both seem to believe that they will benefit if the security crisis here turns into an outright civil war between Shias and Sunnis.
The January election, which for a time seemed to improve the situation, has actually made things more difficult in one way.
Since the Sunnis tended to boycott the vote, the result put political power into the hands of the two other main groups in Iraq, the Shia Muslims and the Kurds.
The US and British governments saw the invasion of Iraq as a liberation, a way of getting rid of a particularly nasty regime. Instead, things are getting much worse.
The casualty figures mean that on average as many people are now dying here every day as were killed in the London bombings nearly two weeks ago.
It has become a civil war, fought out with car bombs and shots to the head, while the foreign forces, US and British and the rest, look on, incapable of stopping it. This isn't how things were supposed to turn out here.
The following comments reflect the balance of opinion we have received so far:
Like others who have responded to Mr Simpson's article, I too ask myself, "Why in the world don't Bush and Blair accept these facts and admit that the US and Britain are losing the peace in Iraq?" Iraq may not be the root cause of terrorism, but it definitely is adding fuel to the fire.
Bill Thomas, Strasbourg, France
Having watched my son, a US Marine, deploy to Iraq and finally return home safely, I have maintained a personal interest in the conflict there. It has been my sense that things are getting worse, and John Simpson, from his perspective as a frequent visitor to Iraq, seems to confirm that. I cannot imagine how Bush and Blair will ever extricate us from the turmoil without leaving a fertile nursery and training ground for terrorists.
Andy Smith, Lake Jackson, Texas, USA
This view of Iraq that John gives is filled with doom and gloom. I have spoken to many US soldiers who have been in Iraq and things are not nearly as bad as this article suggests. War is difficult, but sometimes necessary. Iraq is not a hopeless cause. But these reports are hopelessly negative and in my opinion politically biased.
James, Birmingham, USA
Very nice piece John. It is unfortunate that the security has deteriorated to such a horrific state. I, for one, am proud of the Iraqi people. Despite the dangers they are policing and becoming soldiers to try and secure their home. I am hoping for their success so that they can experience what the rest of the free world experiences everyday.
Maybe our current and future leaders would learn a lesson and not get us in a situation similar to the one we see in Iraq today. As a reluctant supporter of President Bush, however, I believe that his focus must remain on what to do with the current situation in Iraq. Mr Simpson's article offers an honest assessment of this situation, and President Bush has the responsibility to turn this bleak picture into something the Iraqis can live with.
Barry V. Ashar, Windham, NH, USA
Few people can put into words better than Mr Simpson when it comes to explaining the resulting descent of the Iraq situation. You're right Mr Simpson, we are in a world of hurt...
Kurt Stuchell, Cambridge, USA
I lift my hat for Mr Simpson, he is a very brave man and his accounts of the situation in Iraq left us all in no doubt the suffering of the people there. I think there is no going back on Iraq's conflict, it must be finished, only it will take time and more lives but at the end, the remaining Iraqis will realise the benefit of their sacrifices, when they will embrace democracy and freedom.
There was a large support for the war when we first invaded Iraq, but now that the situation is getting worse everybody wants the troops pulled out. We made this mess so it is our responsibility to fix it; I find it unthinkable how some people believe we should pull out just because the situation is proving more difficult than first thought. I can't foresee the situation improving much within the next 5 years, with it more likely to take at least 10 years which most analysts are predicting. To have troops for this length of time would be a huge commitment, but pulling them out at this stage would surely leave the country with only one option, indefinite civil war, with seemingly only one loser, the average Iraqi citizen.
James, Indianapolis, USA
Before the invasion of Iraq, there were only two major problems faced by the world: the Israeli-Palestine conflict and African poverty. Now USA and Britain have created the third problem: Iraq. I feel like the world is becoming a messy place due to the radicalisation and the emergence of the more and more extremists.
Jahangeer K. A., Singapore
I strongly opposed the decision to invade Iraq, but I believe it would be irresponsible to just pull out and leave the majority Iraqi population defenceless against this insanely violent insurgency. I hope we are helping to rebuild the infrastructure. Having said that, I am not hopeful that we will prevail in a guerrilla war in which the opposition is willing to lose every battle and suffer unlimited deaths in order to break our will.
Kerry McCarty, Austin, Tx, USA
This article, and many more clearly show what normal Iraqi citizens have to face day after day. The bread earner has to go out but doesn't know if he will return safely. I think the country may end up splitting into three states namely one for the Kurds, one for the Shias and one for the Sunnis. But breaking up states always means future conflicts.
The US and UK have taken on responsibility for this mess and both countries should work harder to improve the situation. Instead we seem to be trying to ignore the problem and talking about when the troops can leave. I would not like us to pull our troops out until we can guarantee some degree of normality for the Iraqi people.
Remarkable and accurate article. From our own painful daily experience, it must be stated that we, the average middle Iraqis, who are not this or that party or sect member or supporter, are completely hopeless amidst lost dreams of peace and security, progress, development, democracy, and self respect. Saddam did all the basic damage he could on the Iraqi's dignity, and the post-occupation armed and political forces finished up all the rest.
Arif Qaimaqchi, Baghdad, Iraq
I have watched with admiration John Simpson's brave attempts to bring us reports from a host of situations, and his report from Iraq is chilling. When will Bush and Blair and Howard realise that the war is a lost cause?
Brian, Melbourne, Australia
As usual, Mr Simpson hit the nail right on the head. The options for the UK and US are growing fewer by the day. It is obvious that the foreign troops cannot be pulled out now or in the foreseeable future.
Alan S, Herefordshire
Thanks for the article John. It really bothers me to see this going on everyday. We've had 2 minutes silence for London - but what about the people who are dying everyday in Iraq. I can't imagine living in that...