You make the point: "If Kerry gives this answer, Bush turns it around on him viciously. Basically, he paints Kerry as saying the troops are there dying for nothing."

But isn't that the truth? The troops are there dying for nothing.
WHAT ON EARTH ARE THEY DYING FOR?  Kerry just did not have the nerve to fully engage Bush on this issue.  Remember the question -- if we knew THEN what we know NOW.  

What we know now is that neither Iraq nor Saddam was a threat to anyone in anyway.  The problem is that Kerry and the Dems have spent so long appeasing the Republicans and being afraid of them they can no longer distinguish truth from farce.

This should have been his line of attack: Bush lied the country into an unnecessary war for his own vainglory. And THAT would have been the truth. Instead we find ourselves playing on their turf agreeing about how much of a tyrant Saddam was, and removing him was worth 1000 lives and $138 billion.

So yes, our troops are dying for nothing. If you don't agree, please tell me what exactly do you think they are dying for?