Sorry, Aunt mav, I got distracted by an e-mail and forgot to add what I'd meant to.
I think Pres. Bush probably used that word, either by his choice or because he was told to, as a priority: to let either the sponsors of this attack know that the U.S. will not turn the other cheek or let them quietly go back to what they had been doing, as Saddam has, and/or the American public know the same. As someone else posted, he has a responsibility for the well-being of this country, and whether there was ever any actual intent of declaring war or not, I imagine he or his advisors felt that this would be what American citizens needed to hear.

And I really cannot imagine him declaring war--a real declaration of war--on Afghanistan, unless possibly that country claims responsibility for the attack.