The problem is not giving Bush authority once we are at war (though that prospect scares me also), nor is it in amending the list of enemies (though that should be run by congress also, once we are at war I realize that may not always be practical).
The problem is that congress has given Bush complete authority to decide who the enemy is.
What if Bush suddenly has a religious experience and begins to follow Falwell's idea of who caused this war? Bush has already been given authority to take whatever action he thinks is necessary to deal with the 'enemy,' and given total authority to decide who the 'enemy' is.
I think avoiding this very situation was one of the reasons the ability to declare war was given to Congress, not to the president. Congress has in essence handed part of their authority over to Bush.
And yes, I realize that his real power here is limited by political reality. But I prefer to minimize cases where we are depending on one person showing good judgment about things that will affect the entire country forever.
Jay