Dick Morris argues that the explosives story has hurt Kerry much more than Bush. His reasoning is basically that Bush consistently polls far ahead of Kerry on the isses of Iraq and the war on terror. Because of this, he thinks it was crucial for the Kerry people to keep the debate on domestic issues where Kerry polls much closer. Morris thinks that it was a mistake from the beginning to jump on the explosives story because it reminded voters that we have this "war" thing going on and they like Bush better on that issue. When you add in the fact that the whole story is collapsing into a nightmarish web of contradictory stories, the whole thing just makes Kerry look even worse.
Morris's theory sounds plausible, but then again he doesn't have a stellar track record on predictions. Dick Morris is a brilliant man, but sometimes he's often brilliantly wrong.