The bereaved and wounded from Thursday's massacre in Madrid will take little comfort from the observation that the nature and scale of the attack by al-Qaeda (if it was responsible) suggests it is far less a threat than might have been feared after 9/11.
That's the good news. The bad news is that the world has a vulnerability to terrorism that has been barely appreciated.
Compared with the assault on the Twin Towers and the Pentagon Thursday's train bombings in Madrid were small fry. The expectation after 9/11 was that there would be similar spectacular assaults elsewhere in the world, in the US again, in Britain, on mainland Europe, in Saudi Arabia and, of course, Israel.
There have been assaults - in Bali, Casablanca, Saudi Arabia, Mombasa, Istanbul - but nothing on the scale of what happened on 9/11, either in terms of devastation or spectacular. Either al-Qaeda originally had the capacity for just one major operation or the impact of the American and other response in Afghanistan and elsewhere has been such as to degrade its effectiveness. Bombs on rush-hour trains are humdrum, compared with aircraft crashed into skyscrapers, however awful the loss of life and injury.
But there is reason to be gravely concerned, nonetheless. What 9/11 and the other suspected al-Qaeda assaults since then show is that these terrorists are prepared to inflict massive casualties on innocent human beings and, if necessary, to take their own lives in the process. If such terrorists were to acquire access to nuclear weapons there is little doubt that they would use them against civilian targets, in the expectation of inflicting tens (perhaps hundreds) of thousands of casualties.
There is every reason to be apprehensive that terrorists connected with al-Qaeda and otherwise may get such access. And there are two obvious sources of such weapons: Russia and Pakistan.
In an article by three members of International Physicians for the Prevention of Nuclear War, published in the British Medical Journal two years ago (February 9th, 2002) it was noted: "In December 1994 Czech police seized 4kg of highly enriched uranium. During that same year German police seized more than 400g of plutonium. In October 2001 Turkish police arrested two men with 1.16kg of weapons-grade uranium. Also in October 2001 the Russian Defence Ministry reported two recent incidents when terrorist groups attempted to break into Russian storage sites but were repulsed.
"Since 1993 the International Atomic Energy Agency has reported 175 cases of nuclear trafficking, 18 involving highly enriched uranium or plutonium. Even more alarming are reports that small fully-built nuclear weapons are missing from the Russian arsenal."
The Russian nuclear stockpile is huge. Tens of thousands of tactical nuclear warheads and 603 metric tonnes of weapons-grade nuclear material are stored in 53 different sites. The US is helping to finance security at these sites, but only a fraction, for instance, of what it is proposing to spend on a new nuclear missile defence system.
In the meantime, the depleted state of the Russian defence establishment and the inadequacy of resources, coupled with the corruption that is widespread throughout Russian society, mean that this vast arsenal is highly vulnerable to leakage.
There is a terrible irony about the US war on Iraq which, in the words of George Bush, was on the basis that "the United States of America will not permit the world's most dangerous regimes to threaten us with the world's most dangerous weapons". The country the US went to war against, Iraq, had no weapons, whereas the country that was armed with the world's most dangerous weapons and was leaking those weapons around the world, Pakistan, was being pampered and supported by the US.
The "father" of Pakistan's atomic bomb, Abdul Qadeer Khan, along with several others senior in the government of Pakistan, had been leaking nuclear know-how and materials to Libya, Iran and North Korea and probably many other countries and organisations as well. It has now emerged that the CIA told the White House in June 2002 what was going on, but the Bush administration did not want to know.
Pakistan remains the pivot of world security. If Islamic fundamentalists come to power in Pakistan, all bets are off and, to put it at its mildest, the regime of the dictator, Pervez Musharraf, is brittle, as shown by his indulgence of Abdul Qadeer Khan. There will be and could be no invasion, for Pakistan has nuclear weapons. A fundamentalist Pakistan might choose to assist freelance fundamentalists to wage jihad around the world.
The president of Europe (if not too distracted by the revelations of Tom Gilmartin) might like to ponder these matters as he spearheads the war against terrorism whenever he assembles the other European heads of government together. And he might like to wonder whether it might be a good idea, amid the demands for common arrest warrants and European fortresses, to quell the anger of the Islamic world by, for instance, insisting on justice in Israel/Palestine, and a fairer distribution of the world's resources.