I remember thinking soon after Sept. 11th that the War on Terror (as it was quickly labeled) would probably end up a lot like the Cold War: it would be a long, "twilight" struggle where some portion of the political Left (and Right, for that matter) would tire and seek to have us leave the field of battle before we could win. The thing that I thought would be truly distinctive is that, unlike in the Cold War, the Islamists did not and likely would not possess the capability to (a) destroy us or (b) come to rule us. The "Cartoon Wars" and riots in France have made me rethink this a bit - and not in a good way.
Though it may be hard for some people to remember this, the Soviet Union had a real opportunity in the aftermath of WWII to essentially rule all of Europe. Communist parties were quite strong, especially in Italy and France, and if the US had not been willing to spend money (and do whatever else it did) to make sure those parties did not get a hold of power, things could have gone very poorly for us. It's pretty easy to imagine a those parties (who took their orders from Moscow) ordering American troops out of the continent and doing what their brethren in the east did after 1948.
After a while, of course, the threat of direct Soviet rule lessened (they had enough trouble hanging on to their own satellite countries), but still Moscow tried to intimidate the West into bending its direction, at least to the point where they would be "neutral" (a la, say, Finland). The blockade of Berlin, use of communist unions to stage strategic strikes, funding of terrorist groups (Baadher Meinhof Gang, IRA) and "peace" movements, and so on were all designed to apply subtle (and not so subtle) pressure on western Europe in an effort to divide them from the US and bend them (ever so slightly) to the Soviet will. (There were, of course, genuinely home-grown movements that wanted the same thing).
It strikes me that this is precisely the same sort of thing that is going on now in regards to Europe and the Islamists. They can't rule outright - there aren't enough of them - but they can intimidate European governments and societies enough such that the US has to consider much of Europe simply unreliable when it comes to policy toward the Middle East. I have no doubt that the Europeans definitely do not want Iran to get a nuke (they are, after all, much closer than we are), but if push comes to shove, can the Europeans be depended upon to help with action (i.e. reducing every Iranian military facility to rubble)? If a few enterprising Imams can intimidate most European governments into helpless sputtering on the basis of some unremarkable cartoons, what do you think they'll do when it becomes clear that we're getting ready to take Iran out?
I'm still convinced that the Islamists don't pose the same degree of strategic threat that the Soviets did - they just don't have 2,000 ICBMs. But they can intimidate our allies (and us) enough to make it easier for them to win control of the Islamic countries in the Middle East. And that's a cause for worry.