No, I'm taking the term "Declare War" literally, as it was said that since WW II, the US government has declared war in many ways. Which is untrue as we have not officially declared war since WW II. Even on things not "War on Terror". We've attacked sovereign countries without declaration of war. Terrorists may be able to hide out in many places, however, taking out say the sovereign government of Iraq had nothing to do with that. In fact, that was war against another sovereign nation without declaration of war.
There are many limitations within the Constitution, and those limitations were there for a reason. I happen to be of the mind that using those limitations is wise.
You know what, I would prefer the US didn't go dropping bombs on sovereign nations too. I would prefer it if nations with a terrorist presence took care of it themselves. Take a look at the Philippines and Jordan. Both have a terrorist presence and they've done quite a good job of smashing hard on that presence. The US is not dropping bombs on either country. Isn't that nice?
I know what the counter-argument will be: "But they're allies of the US and that's why the US isn't there." Yes, a strange coincidence isn't it? Countries inimical to the US, that wouldn't shed a tear if the US "suffered a mishap," tend to also be the ones who place mass-murderers in palaces and otherwise provide them with a safe-haven. One might confuse this with harboring and supporting Terrorism. And if that terrorist publicly announces he intends to kill Americans (or anyone else) that's like keeping a weapon specifically intended for use on the US (or anyone else), even though they never declared war. That's...not nice, is it?
It doesn't matter so much that they don't like us. It matters more that they are keeping what amounts to a weapon of mass destruction in the form of a malignant human mind, available for use as a weapon against the citizens of the USA. What's unique about the terrorist mind as a weapon is the hosting nation can use this weapon upon innocents over an over again and claim that it made no attack upon the US or other nations, thus eliminating the possibility of "legal retribution."
That's what they're hoping for anyway. They hope that the American sense of fair play, of "due process," of following legal procedures rigidly, will paralyze us into inaction. If we stuck rigidly to constitutional doctrine as you suggest, we could only do anything "after" terrorist attacks are already killing innocents. Its playing straight into their hands and we will have absolutely no other recourse other than just take it and suffer quietly like little pansies. If we demonstrate a little flexibility and foresight, we can destroy that human weapon "before" it is employed. When doing this we have a responsibility to destroy that weapon with absolutely minimum foreign civilian casualties, but we must be certain that we do it.
The terrorists "want" us to be stuck. They "want" us to wring our hands and whine pitiably, uncertain what action to take because the Constitution doesn't tell us what to do. They "want" us to stand on our "moral high ground" while they are allowed to kill innocent after innocent with absolute impunity. They believe we have no common sense at all and if we place "their" rights above the rights of "our own innocents," we will have proven them correct.