I agree that how close to the election it occurs will be a factor. Not only because it gives Kerry/?????

time to react, as I mentioned above, but because it will distance people from the emotional reaction, which I think I neglected.
But I don't think it will be because Americans will want action. They (we) will, but I don't think that'll be the defining factor. I think most Americans are glad we took action after 9/11. If Bush is in trouble on terrorism, it's because he hasn't taken enough action, or has taken the wrong actions, and the results of his actions are making the difference. But if you asked today, we're we right to topple the Taliban, I think most Americans, even most Democrats would say, Hell yes!
That said, it will help Bush that people know he will take action (even if it's wrong) and some may doubt that Kerry will. I've heard an awful lot of people, even ones leaning to Kerry now, who are afraid Gore would not have done anything. I think they're nuts, but they exist.
The big danger to Kerry and the election, tho, will be pure cussedness. If there is a terrorist attack, esp one close to Nov 2nd, people will believe al Qaeda did it to influence the election (but in the way it happened in Spain--they mostly refuse to realize how smart these people are). They will vote for Bush just to show the terrorists we won't let them elect Kerry. It's crazy. It's perverse. But it's the way it will go down. I'd bet real money on it.
Already, we hear the RNC meme that the terrorists want Kerry to win and a helluva lot of people are concerned about that. It goes back to the whole "Democrats are weak on defense" fears and prejudices.
Not every voter thinks like a Democrat.