I disagree with this. I believe it will make us staunch Bush-supporters even more sure of our convictions, but we only have one vote, no matter how strongly we feel about it.
I share an office with a lunatic liberal, and if there was a terrorist attack, to her, it would be PROOF of how badly Bush has handled "this whole Iraq debacle." (their words, NOT mine)
So I think a terrorist attack is more likely to swing people AWAY from Bush than towards him. After all, for those with their heads in the sand, they can say "First September 11, and now THIS, and both on Bush's watch? I'm not voting for Bush!!"
The problem lies in your own words -- "lunatic liberal." She wouldn't vote for Bush if he was the Messiah. I think the voters in the middle may sway his way, depending on how it was handled by the administration.
That being said, I hope it doesn't happen in the first place!