He should definitely be attacked on the real issues, but he shouldn't be allowed to get away with this, either. If we call him on it now, at least he probably won't try it again.
There is nothing to be proven here. Kerry pulled an object, be it paper, cards, handkerchief from his pocket. None of those things were allowed. This was done in full view of the camera (that he apparently didn't know about). It will now be a spin war. No matter what the Kerry camp says, the suspicion about what he had will remain.