"What has happened since 9/11 that comes anywhere close to the magnitude of 9/11? "
Nothing yet. But listening to Cheney, Ridge, et al, it's only a matter of time, regardless of what we do in Iraq before we get hit again. Hell, Bush himself admitted that the WOT is probably not winnable, in one of the more candid quotes of his first term. I mean, what do you do - kill every single Muslim on the planet? Impossible and immoral.
As open as our country is I have expected another large scale attack ever since 9/11. I see nothing that we can do to prevent determined terrorists who are willing to die in order to attack us.
Our southern border is open and the northern one isn't any better.