The short answer to this question is yes and no. Yes, in the sense that terrorism was never a global phenomenon that could be defeated by a "war" as proposed by George W. Bush. No, in the sense that the United States will be attacked again someplace, sometime.
For those who say that the $40 to $50 billion we spend each year on homeland security has achieved its purpose, namely that we have not been attacked again, it is only necessary to remind ourselves that eight years passed between the first and second attacks on the World Trade Center and eight years have passed, today, since 9/11. So, for those of us who, like Richard Clarke, have always had "our hair on fire," another attack by some group, probably related in some way to al Qaeda, is to be expected.
On a scale of 1 to 10, we are not yet at 9, or probably even 7. The greatest danger in terms of potential damage to life and property is still the nuclear threat. But if, as I suspect, the most likely and easiest future attack involves biological agents, our borders are and will remain porous, defenses against viral agents borne by human "bombs" are and will remain inadequate, and post-attack response is insufficient. Response plans, involving quarantine, suppression, mass casualty victim treatment, and other measures can always use improvement.
And, though we happily haven't heard it lately, the false security brought on by the nonsensical maxim "we're fighting them over there so we don't have to fight them here" is exactly that: false.
By abandoning the "war on terrorism" paradigm, especially as an excuse to invade Iraq, President Obama has done our strategy a favor and has taken us a long way toward the understanding that acts of terrorism will continue in parts of the world, that we must continue to make such acts as difficult as possible here in the United States, that most attacks will still be against other countries, and that quick damage-limitation response at home will still be highly important.
As we remember those who died, unnecessarily, eight years ago, let us also continue to combine vigilance with realistic appreciation for the new age of the 21st century in which we live.