The possibility, likelihood even, that, after all, al-Qaeda was responsible for the Madrid bombings brings Europe face-to-face with a new reality.
It has taken time for this to sink in. In the immediate aftermath of the Madrid attacks, it was not only the Spanish government who was blaming Eta.
People across Europe are wondering who will be next
Many experts in the intelligence field did as well. And they did not have, as the Spanish government did, a vested interest in the blaming the Basques.
They had some circumstantial evidence on their side. Eta had previously put a bomb on a train and had a huge consignment of explosives intercepted en route to Madrid recently, it was pointed out.
It therefore had a plan and the intention to carry it out. Even the Spanish crackdown on Eta was used as a possible explanation. A new leadership might have taken over, it was suggested, made up of younger and more ruthless people.
There seemed to be a collective desire in the intelligence community not to accept that a new Islamist front might have been opened up in Western Europe.
Perhaps ordinary people were quicker to suspect what was going on - that if it looked like al-Qaeda and acted like al-Qaeda, then it probably was al-Qaeda.
We still do not know the truth, of course, which makes comment on the bombings more than usually risky.
But will governments change policies?
But even if the al-Qaeda theory fades in this case, Europe is still faced with the Islamist threat. And if it is confirmed, then the dangers are closer than ever.
And the implications are huge.
First, there is the issue of whether governments will change their policies to try to placate the bombers or whether they will continue as before.
Could a government carry on "business as usual" after maybe two or three massive attacks? Governments always say that we must not "surrender to terrorism".
But if some countries are not targeted because they did not support the war in Iraq, the others might find it convenient to trim their sails. Political leaders often cry no surrender in public but look for solutions in private.
The tactics of how to wage a war on terrorism are already dividing American society in its election year. In Europe, there are even more doubts. So, does a government gain electorally by being militant or by being pacifist?
A second issue is that of civil liberties. The UK Home Secretary David Blunkett says bluntly that he prefers to be tough now rather then be blamed later.
London 'a target'
But what would happen if he proposed a system of imprisonment without trial which applied not just to foreign citizens, as it currently does, but to Britons as well?
It was tried in Northern Ireland with disastrous effect but that was a different time and place and this time internment might be more sophisticated, with reviews and time limits for example. It would still be controversial. And would it be tolerated?
A third consideration is security and how far the citizenry will accept disruption of ordinary life. The idea of being searched before getting on a train seems to many absurd. It might simply displace the target in any case and transfer death somewhere else.
People may be searched before boarding trains
It could not apply to the London Underground without seizing up the whole network and the Underground frankly remains a likely target in London.
It may be that Western Europe just tries to carry on as normal, trusting the police and intelligence services to do their job.
The trouble with that is that in Spain they failed.
It does not take many determined and expert terrorists to cause havoc if they are sufficiently ruthless.
In this new reality there are no easy answers.