You should start an office pool. I think one more September 11-type attack would do the trick, but you may be right if the attacks were "smaller" with limited damage/deaths. I have also thought that since Al Qaeda must be reading the (doctored) opinion polls on Iraq, they might be more interested in striking "infrastructure" targets, rather than people per se. This would produce feelings of insecurity, give the Leftists something to crow about, but would not risk violating Napoleon's dictum to "never interrupt your enemy when he is making a mistake", by inflicting the kinds of civilian casualties that might unite the American people behind President Bush.
RE: another September 11 attack. Next time, it may be a cruise ship with 3,000 passengers and 1500 crew. Those things have as many holes in them, security-wise, as a sieve.
I watched the extremely corny "Poseidon Adventure" last night, and it was very melodramatic. Nevertheless, they showed accurately how easy it would be for Al Quaeda to get their agents in place on a cruise ship.